[compiler-rt] [llvm] [X86][BF16] Add libcall for F80 -> BF16 (PR #109116)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-offload-libc-amdgpu-runtime` running on `omp-vega20-1` while building `compiler-rt,llvm` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/5720

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (compile-openmp) failure: build (failure)
...
0.249 [142/34/143] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/addvsi3.c.o
0.250 [141/34/144] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/ashlti3.c.o
0.251 [140/34/145] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/ashrdi3.c.o
0.252 [139/34/146] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/floatdixf.S.o
0.252 [138/34/147] Building ASM object CMakeFiles/clang_rt.builtins-i386.dir/i386/floatundixf.S.o
0.252 [137/34/148] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/addvti3.c.o
0.252 [136/34/149] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/ashrti3.c.o
0.257 [135/34/150] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/bswapsi2.c.o
0.258 [134/34/151] Building C object CMakeFiles/clang_rt.builtins-i386.dir/mulxc3.c.o
0.258 [133/34/152] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o
FAILED: CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o 
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.build/./bin/clang --target=x86_64-unknown-linux-gnu -DVISIBILITY_HIDDEN  -O3 -DNDEBUG -m32 -fno-lto -std=c11 -fPIC -fno-builtin -fvisibility=hidden -fomit-frame-pointer -DCOMPILER_RT_HAS_FLOAT16 -MD -MT CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o -MF CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o.d -o CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o -c /home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/truncxfbf2.c
In file included from /home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/truncxfbf2.c:11:
In file included from /home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc_impl.inc:39:
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:49:2: error: Source should be double precision or quad precision!
   49 | #error Source should be double precision or quad precision!
      |  ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:114:15: error: unknown type name 'src_rep_t'; did you mean 'dst_rep_t'?
  114 | static inline src_rep_t extract_sign_from_src(src_rep_t x) {
      |               ^~~~~~~~~
      |               dst_rep_t
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:114:47: error: unknown type name 'src_rep_t'; did you mean 'dst_rep_t'?
  114 | static inline src_rep_t extract_sign_from_src(src_rep_t x) {
      |                                               ^~~~~~~~~
      |                                               dst_rep_t
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:115:9: error: unknown type name 'src_rep_t'; did you mean 'dst_rep_t'?
  115 |   const src_rep_t srcSignMask = SRC_REP_C(1) << (srcBits - 1);
      |         ^~~~~~~~~
      |         dst_rep_t
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:115:33: error: call to undeclared function 'SRC_REP_C'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  115 |   const src_rep_t srcSignMask = SRC_REP_C(1) << (srcBits - 1);
      |                                 ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:115:50: error: use of undeclared identifier 'srcBits'; did you mean 'dstBits'?
  115 |   const src_rep_t srcSignMask = SRC_REP_C(1) << (srcBits - 1);
      |                                                  ^~~~~~~
      |                                                  dstBits
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:101:18: note: 'dstBits' declared here
  101 | static const int dstBits = sizeof(dst_t) * CHAR_BIT;
      |                  ^
/home/ompworker/bbot/openmp-offload-libc-amdgpu-runtime/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:116:32: error: use of undeclared identifier 'srcBits'; did you mean 'dstBits'?

```

</details>

https://github.com/llvm/llvm-project/pull/109116