Add support for IPOPT on Mac by pinning to a specific GCC version.

[david-german-tri]

This makes it possible to locate libgfortran.a on Mac, since Homebrew doesn't install or symlink it to a canonical location. It would be much better to use pkg-config, but Homebrew doesn't install a .pc file. It would also be much better to interrogate gfortran directly, as IPOPT itself does, but Bazel apparently provides no mechanism to use the results of a shell command as linker arguments to a cc_library rule.

@soonho-tri for feature review; could you test locally please?

@jamiesnape @BetsyMcPhail The OS X images in CI should be updated to pin gcc 5.4, instead of tracking the head of gcc. Aside and apart from the Bazel issue, I think it's saner to use a version of gfortran on Mac that's consistent with the project's other uses of gcc.

Also, if anyone knows of a way to make brew pin more precise, that would be great.

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This change is 

[soonho-tri]

@soonho-tri for feature review; could you test locally please?

Sure. BTW, I don't see the reviewable link here.

[soonho-tri]

Never mind. Just created!

[soonho-tri]

Review status: 0 of 3 files reviewed at latest revision, 1 unresolved discussion.

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a discussion (no related file):
I have the following error on my mac:

$ bazel test //... -c dbg
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/drake_visualizer/BUILD:2:48: soft_failure.bzl: @drake_visualizer//:drake-visualizer does not work because /Users/soonhok/work/drake-distro/build/install/bin/drake-visualizer was missing.
ERROR: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD:121:36: name 'HOMEBREW_GFORTRAN_PATH' is not defined.
ERROR: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD:134:27: Traceback (most recent call last):
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 127
		cc_library(name = "lib", srcs = IPOPT_LIBS, hdr..., <5 more arguments>)
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 132, in cc_library
		select({"//config:linux": LINKOPTS_LINU...})
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 134, in select
		LINKOPTS_APPLE
name 'LINKOPTS_APPLE' is not defined.
ERROR: /Users/soonhok/work/drake-distro/drake/solvers/BUILD:175:1: no such target '@ipopt//:lib': target 'lib' not declared in package '' defined by /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD and referenced by '//drake/solvers:ipopt_solver'.
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/protobuf_python/protobuf.bzl:90:19: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/protobuf_python/protobuf.bzl:96:28: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
ERROR: Analysis of target '//drake/systems/trajectory_optimization:direct_collocation' failed; build aborted.
INFO: Elapsed time: 2.971s
ERROR: Couldn't start the build. Unable to run tests.

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Comments from Reviewable

[soonho-tri]

Review status: 0 of 3 files reviewed at latest revision, 1 unresolved discussion.

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a discussion (no related file):

Previously, soonho-tri (Soonho Kong) wrote…

I have the following error on my mac:

$ bazel test //... -c dbg
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/drake_visualizer/BUILD:2:48: soft_failure.bzl: @drake_visualizer//:drake-visualizer does not work because /Users/soonhok/work/drake-distro/build/install/bin/drake-visualizer was missing.
ERROR: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD:121:36: name 'HOMEBREW_GFORTRAN_PATH' is not defined.
ERROR: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD:134:27: Traceback (most recent call last):
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 127
		cc_library(name = "lib", srcs = IPOPT_LIBS, hdr..., <5 more arguments>)
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 132, in cc_library
		select({"//config:linux": LINKOPTS_LINU...})
	File "/private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD", line 134, in select
		LINKOPTS_APPLE
name 'LINKOPTS_APPLE' is not defined.
ERROR: /Users/soonhok/work/drake-distro/drake/solvers/BUILD:175:1: no such target '@ipopt//:lib': target 'lib' not declared in package '' defined by /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/ipopt/BUILD and referenced by '//drake/solvers:ipopt_solver'.
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/protobuf_python/protobuf.bzl:90:19: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
WARNING: /private/var/tmp/_bazel_soonhok/51e1ef8bb59598000e1968965dd33f03/external/protobuf_python/protobuf.bzl:96:28: Variables HOST_CFG and DATA_CFG are deprecated in favor of strings "host" and "data" correspondingly.
ERROR: Analysis of target '//drake/systems/trajectory_optimization:direct_collocation' failed; build aborted.
INFO: Elapsed time: 2.971s
ERROR: Couldn't start the build. Unable to run tests.

On another mac, it works well.

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Comments from Reviewable

[david-german-tri]

Yeah, sorry, I also am having difficulties after making changes based on the Slack conversation. Stay tuned.

[soonho-tri]

No need to sorry at all. Thanks a lot for the hard work!!

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Review status: 0 of 3 files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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Comments from Reviewable

[drake-jenkins-bot]

Jenkins build failed

[david-german-tri]

I'm closing this - @jwnimmer-tri has made a better suggestion, namely to use a repository rule. I'd somehow forgotten repository rules could capture shell command outputs.

[drake-jenkins-bot]

Jenkins build failed

[drake-jenkins-bot]

Jenkins build passed