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.

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

• ✔️ behavior, std lib, and compiler-rt tests for armv8_5a-linux-none
• ✔️ behavior, std lib, and compiler-rt tests for armv8_5a-linux-musl, statically linking against a zig-built musl. Disabled due to unable to build musl for target armv8-linux-musleabihf #3286.
• ❌ behavior, std lib, and compiler-rt tests for armv8_5a-linux-gnu, dynamically linking against a zig-built glibc. Disabled due to unable to build glibc for target armv8-linux-gnueabihf  #3287.

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

• std lib tests failing on arm 32-bit #3289
• Cannot compile Zig source for target armv7-linux-musleabi #2833
• Constant packed struct instantiations can generate incorrect unaligned loads on armv4t/armv5 #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.