[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 `clang-x86_64-debian-fast` running on `gribozavr4` while building `compiler-rt,llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/7705

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
0.098 [70/98/151] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/clzti2.c.o
0.099 [69/98/152] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/cmpdi2.c.o
0.100 [68/98/153] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/cmpti2.c.o
0.104 [67/98/154] Building C object CMakeFiles/clang_rt.builtins-i386.dir/divdc3.c.o
0.104 [66/98/155] Building C object CMakeFiles/clang_rt.builtins-i386.dir/muldf3.c.o
0.105 [65/98/156] Building C object CMakeFiles/clang_rt.builtins-i386.dir/udivmoddi4.c.o
0.105 [64/98/157] Building C object CMakeFiles/clang_rt.builtins-i386.dir/emutls.c.o
0.105 [63/98/158] Building C object CMakeFiles/clang_rt.builtins-i386.dir/mulxc3.c.o
0.105 [62/98/159] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncdfbf2.c.o
0.106 [61/98/160] Building C object CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o
FAILED: CMakeFiles/clang_rt.builtins-i386.dir/truncxfbf2.c.o 
/b/1/clang-x86_64-debian-fast/llvm.obj/./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 /b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/truncxfbf2.c
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/truncxfbf2.c:11:
In file included from /b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/fp_trunc_impl.inc:39:
/b/1/clang-x86_64-debian-fast/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!
      |  ^
/b/1/clang-x86_64-debian-fast/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
/b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/b/1/clang-x86_64-debian-fast/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
/b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/b/1/clang-x86_64-debian-fast/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
/b/1/clang-x86_64-debian-fast/llvm.src/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/b/1/clang-x86_64-debian-fast/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);
      |                                 ^
/b/1/clang-x86_64-debian-fast/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
/b/1/clang-x86_64-debian-fast/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;
      |                  ^
/b/1/clang-x86_64-debian-fast/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