[clang] [Driver] Teach Barmetal toolchain about GCC installation (PR #121829)

[Peter Smith via cfe-commits]

================
@@ -0,0 +1,12 @@
+// check that gnu assembler is invoked with arm baremetal as well
+
+// RUN: %clang --target=armv6m-none-eabi  --gcc-toolchain=%S/Inputs/basic_riscv32_tree -fno-integrated-as %s -### -c \
----------------
smithp35 wrote:

I'm a bit confused about this test. It is called `arm-gnutools.c`, but has both arm and aarch64 triples, and uses a `basic_riscv32 tree`.

Is it just that we're using `basic_riscv32_tree` to tell the driver that it is in GNU "mode" so look for `<triple>-as` 

Could be worth a comment if that's the case. There's a possibility that the driver could actually look for the exectuable in the GCC toolchain. 

https://github.com/llvm/llvm-project/pull/121829