llvm: Implement sub-architecture translation in targetTriple().

[alexrp]

Addresses this problem: ziglang/zig-bootstrap#102 (comment)

[alexrp]

A neat side effect here is that #10411 is significantly alleviated. For example, I can now build libffi for Arm soft float targets:

❯ zig3 build -Dtarget=arm-linux-gnueabi
install
└─ install ffi
   └─ zig build-lib ffi Debug arm-linux-gnueabi 1 errors
/home/alexrp/Source/vezel-dev/libffi/src/arm/sysv.S:1:1: error: clang exited with code 1
error: error(compilation): clang failed with stderr: /home/alexrp/Source/vezel-dev/libffi/src/arm/sysv.S:167:2: error: instruction requires: armv5t
 blx lr @ call fn
 ^


error: the following command failed with 1 compilation errors:
/home/alexrp/Source/zig/build/debug/bin/zig build-lib -cflags -fexceptions -- /home/alexrp/Source/vezel-dev/libffi/src/closures.c /home/alexrp/Source/vezel-dev/libffi/src/java_raw_api.c /home/alexrp/Source/vezel-dev/libffi/src/prep_cif.c /home/alexrp/Source/vezel-dev/libffi/src/raw_api.c /home/alexrp/Source/vezel-dev/libffi/src/tramp.c /home/alexrp/Source/vezel-dev/libffi/src/types.c -cflags -fexceptions -- /home/alexrp/Source/vezel-dev/libffi/src/arm/ffi.c /home/alexrp/Source/vezel-dev/libffi/src/arm/sysv.S -ODebug -target arm-linux-gnueabi -mcpu baseline -I /home/alexrp/Source/vezel-dev/libffi/include -I /home/alexrp/Source/vezel-dev/libffi/src -I /home/alexrp/Source/vezel-dev/libffi/src/arm -I /home/alexrp/Source/vezel-dev/libffi/.zig-cache/o/3b1d40f9694c554307ff61b4c48f350f/ -I /home/alexrp/Source/vezel-dev/libffi/.zig-cache/o/02b1253f3139eca6241e4d644e83704b/ -Mroot -lc --cache-dir /home/alexrp/Source/vezel-dev/libffi/.zig-cache --global-cache-dir /home/alexrp/.cache/zig --name ffi -static --zig-lib-dir /home/alexrp/Source/zig/lib/ --listen=-
Build Summary: 2/5 steps succeeded; 1 failed
install transitive failure
└─ install ffi transitive failure
   └─ zig build-lib ffi Debug arm-linux-gnueabi 1 errors
error: the following build command failed with exit code 1:
/home/alexrp/Source/vezel-dev/libffi/.zig-cache/o/2057d466747404c7de931ecab5bce90d/build /home/alexrp/Source/zig/build/debug/bin/zig /home/alexrp/Source/zig/lib /home/alexrp/Source/vezel-dev/libffi /home/alexrp/Source/vezel-dev/libffi/.zig-cache /home/alexrp/.cache/zig --seed 0x14ecf161 -Z48792836574354d5 -Dtarget=arm-linux-gnueabi
❯ zig4 build -Dtarget=arm-linux-gnueabi
❯

It's still not properly fixed, of course, but passing the sub-architecture helps to enable instructions that would otherwise be disabled because the default for arm-linux-gnueabi is armv4t.

[andrewrk]

Nice!