Revert "Reland "[compiler-rt][BF16] Provide __truncsfbf2 only when __bf16 is available""

This reverts commit 0729d00135.

Buildbot https://lab.llvm.org/buildbot/#/builders/19/builds/11989 failed
with "error: ISO C requires a translation unit to contain at least one declaration [-Werror,-Wempty-translation-unit]"

compiler-rt/cmake/builtin-config-ix.cmake

@@ -30,14 +30,6 @@ _Float16 foo(_Float16 x) {
 "
 )
 
-builtin_check_c_compiler_source(COMPILER_RT_HAS_BFLOAT16
-"
-__bf16 foo(__bf16 x) {
- return x;
-}
-"
-)
-
 builtin_check_c_compiler_source(COMPILER_RT_HAS_ASM_LSE
 "
 asm(\".arch armv8-a+lse\");

compiler-rt/lib/builtins/CMakeLists.txt

@@ -699,8 +699,6 @@ else ()
 
   append_list_if(COMPILER_RT_HAS_FLOAT16 -DCOMPILER_RT_HAS_FLOAT16 BUILTIN_CFLAGS)
 
-  append_list_if(COMPILER_RT_HAS_BFLOAT16 -DCOMPILER_RT_HAS_BFLOAT16 BUILTIN_CFLAGS)
-
   append_list_if(COMPILER_RT_HAS_STD_C11_FLAG -std=c11 BUILTIN_CFLAGS)
 
   # These flags would normally be added to CMAKE_C_FLAGS by the llvm

compiler-rt/lib/builtins/fp_trunc.h

@@ -60,7 +60,7 @@ typedef uint16_t dst_rep_t;
 static const int dstSigBits = 10;
 
 #elif defined DST_BFLOAT
-typedef __bf16 dst_t;
+typedef uint16_t dst_t;
 typedef uint16_t dst_rep_t;
 #define DST_REP_C UINT16_C
 static const int dstSigBits = 7;

compiler-rt/lib/builtins/truncdfbf2.c

@@ -6,11 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(COMPILER_RT_HAS_BFLOAT16)
 #define SRC_DOUBLE
 #define DST_BFLOAT
 #include "fp_trunc_impl.inc"
 
 COMPILER_RT_ABI dst_t __truncdfbf2(double a) { return __truncXfYf2__(a); }
-
-#endif

compiler-rt/lib/builtins/truncsfbf2.c

@@ -6,11 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(COMPILER_RT_HAS_BFLOAT16)
 #define SRC_SINGLE
 #define DST_BFLOAT
 #include "fp_trunc_impl.inc"
 
 COMPILER_RT_ABI dst_t __truncsfbf2(float a) { return __truncXfYf2__(a); }
-
-#endif