[libclc] Remove -fno-builtin from compile options

The flag was added in commit 5631a959571c 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}