Tier 1 Support for ARM 32-bit Linux

[andrewrk]

Once all these items are complete, we can say that Zig has Tier 1 support for 32-bit ARM Linux.

• [x] make sure we can build-exe with -target armv7-linux-gnu
• [x] make sure we can build-exe with -target armv7-linux-musleabihf
• [ ] test coverage for stack traces / debug info
• [x] add the target to the test matrix
• [ ] get the full test suite passing
• [x] figure out a 32-bit arm linux continuous integration testing service and hook it up to zig's CI testing.
• [ ] #9947

For 64-bit ARM Linux support, see #2443

[andrewrk]

With the merge of #3290, we now have userland qemu-based Continuous Integration test coverage for:

• :heavy_check_mark: behavior, std lib, and compiler-rt tests for armv8_5a-linux-none
• :heavy_check_mark: behavior, std lib, and compiler-rt tests for armv8_5a-linux-musl, statically linking against a zig-built musl. ~Disabled due to #3286.~
• :x: behavior, std lib, and compiler-rt tests for armv8_5a-linux-gnu, dynamically linking against a zig-built glibc. Disabled due to #3287.

In addition to the above issues, the remaining issues to solve are:

• #3289
• #2833
• #2767

Once these are solved, and we add test coverage for stack traces on arm-linux, 32-bit ARM linux can be promoted to a Tier 1 Supported target.

[link2xt]

-target armv7-linux-musleabihf

Isn't it named arm-linux-musleabihf? Trying to compile C code with zig cc -target armv7-linux-musleabihf I get error: UnknownArchitecture.