[libclc] Remove -fno-builtin from compile options (#162075)

The flag was added in 8ef48d0 to suppress build warning and is no
longer needed.

It adds "no-builtins" attribute, which prevents libclc functions from
being inlined into caller that don't have the attribute.

The flag is meant to prevent folding standard library calls into
optimized implementations. For libclc device targets, however, such
target‑driven folding is desirable.

llvm-diff shows no change to amdgcn--amdhsa.bc and nvptx--nvidiacl.bc.

Co-authored-by: Mészáros Gergely <[email protected]>

Author: wenju-he

libclc/cmake/modules/AddLibclc.cmake

@@ -353,7 +353,7 @@ function(add_libclc_builtin_set)
       TRIPLE ${ARG_TRIPLE}
       INPUT ${input_file}
       OUTPUT ${output_file}
-      EXTRA_OPTS -fno-builtin -nostdlib "${ARG_COMPILE_FLAGS}"
+      EXTRA_OPTS -nostdlib "${ARG_COMPILE_FLAGS}"
         "${file_specific_compile_options}"
         -I${CMAKE_CURRENT_SOURCE_DIR}/${file_dir}
       DEPENDENCIES ${input_file_dep}