[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-linux-abi-test` running on `sie-linux-worker2` while building `compiler-rt,llvm` at step 6 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/8/builds/4662

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

```
Step 6 (build-unified-tree) failure: build (failure)
...
2.092 [4/10/159] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/floatuntixf.c.o
2.101 [3/10/160] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatdixf.c.o
2.124 [2/10/161] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/fixunsxfti.c.o
2.125 [1/10/162] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/mulxc3.c.o
2.131 [1/9/163] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/powixf2.c.o
2.173 [1/8/164] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/truncdfbf2.c.o
2.173 [1/7/165] Building C object clang_rt.crtbegin.o
2.197 [1/6/166] Building ASM object CMakeFiles/clang_rt.builtins-x86_64.dir/x86_64/floatundixf.S.o
2.198 [1/5/167] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/extendbfsf2.c.o
2.201 [1/4/168] Building C object CMakeFiles/clang_rt.builtins-x86_64.dir/truncxfbf2.c.o
FAILED: CMakeFiles/clang_rt.builtins-x86_64.dir/truncxfbf2.c.o 
/home/buildbot/buildbot-root/abi-test/build/./bin/clang --target=x86_64-unknown-linux-gnu -DVISIBILITY_HIDDEN  -O3 -DNDEBUG -m64 -fno-lto -std=c11 -fPIC -fno-builtin -fvisibility=hidden -fomit-frame-pointer -DCOMPILER_RT_HAS_FLOAT16 -MD -MT CMakeFiles/clang_rt.builtins-x86_64.dir/truncxfbf2.c.o -MF CMakeFiles/clang_rt.builtins-x86_64.dir/truncxfbf2.c.o.d -o CMakeFiles/clang_rt.builtins-x86_64.dir/truncxfbf2.c.o -c /home/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/truncxfbf2.c
In file included from /home/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/truncxfbf2.c:11:
In file included from /home/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/fp_trunc_impl.inc:39:
/home/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/fp_trunc.h:99:18: note: 'dst_rep_t' declared here
   99 | typedef uint16_t dst_rep_t;
      |                  ^
/home/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/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/buildbot/buildbot-root/abi-test/llvm/compiler-rt/lib/builtins/fp_trunc.h:101:18: note: 'dstBits' declared here
  101 | static const int dstBits = sizeof(dst_t) * CHAR_BIT;
      |                  ^
/home/buildbot/buildbot-root/abi-test/llvm/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