Runtime checks on registry file generation and add ability to run out-of-source

[islas]

TYPE: bug fix

KEYWORDS: registry, out-of-source

SOURCE: internal

DESCRIPTION OF CHANGES:
Problem:
Registry code generation continues regardless of errors and missing fields are not caught until sometimes ~40 minutes into compilation when a subsequent source file is missing registry-generated fields. Additionally, the generated code clutters the source development environment with hundreds of files, requiring many .gitignore entries that seem counterintuitive (e,g. ignoring all *.f90 source files). Finally, there is a bug in the the gen_allocs conditionally compiled code

Solution:
Check returns of gen_...() functions that create files to output if respective call failed to generate the registry code
Add the ability to supply a root registry directory to utilize instead of assumed relative directories to allow out-of-source registry code generation outside of the WRF repo. Make assumed relative still the default method so previous builds not using this new capability still work.
Fix gen_allocs.c define macro

LIST OF MODIFIED FILES:
M tools/gen_allocs.c
M tools/gen_streams.c
M tools/reg_parse.c
M tools/registry.c

TESTS CONDUCTED:

1. Do mods fix problem? Local compilation demonstrates fixes working as expected
2. Are the Jenkins tests all passing? Yes

RELEASE NOTE:
Runtime checks on registry file generation and add ability to run out-of-source. Minor bug fix in gen_allocs.c

[islas]

@dudhia @weiwangncar
At the suggesting of @mgduda I've split #1899 into more digestible PRs addressing individual issues

[weiwangncar]

The regtest results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

[mgduda]

I'd suggest splitting this PR into three separate PRs:

• registry code generation should fail if an error is encountered
• one-line fix for bug in gen_allocs
• support out-of-source builds

[islas]

three separate PRs

Will close this one and open new ones shortly