[libc] Fix flag parsing bugs. (#84706)

libc/cmake/modules/LLVMLibCCompileOptionRules.cmake

diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index 72b0482..893a807 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -2,10 +2,10 @@
   set(compile_options "")
 
   if(LIBC_TARGET_ARCHITECTURE_IS_RISCV64 OR(LIBC_CPU_FEATURES MATCHES "FMA"))
-    check_flag(ADD_FMA_FLAG ${FMA_OPT_FLAG} ${flags})
+    check_flag(ADD_FMA_FLAG ${FMA_OPT_FLAG} ${ARGN})
   endif()
-  check_flag(ADD_SSE4_2_FLAG ${ROUND_OPT_FLAG} ${flags})
-  check_flag(ADD_EXPLICIT_SIMD_OPT_FLAG ${EXPLICIT_SIMD_OPT_FLAG} ${flags})
+  check_flag(ADD_SSE4_2_FLAG ${ROUND_OPT_FLAG} ${ARGN})
+  check_flag(ADD_EXPLICIT_SIMD_OPT_FLAG ${EXPLICIT_SIMD_OPT_FLAG} ${ARGN})
 
   if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
     if(ADD_FMA_FLAG)

libc/cmake/modules/LLVMLibCFlagRules.cmake

diff --git a/libc/cmake/modules/LLVMLibCFlagRules.cmake b/libc/cmake/modules/LLVMLibCFlagRules.cmake
index 9bec716..18e36df 100644
--- a/libc/cmake/modules/LLVMLibCFlagRules.cmake
+++ b/libc/cmake/modules/LLVMLibCFlagRules.cmake
@@ -131,9 +131,9 @@
 
 # Check if a `flag` is set
 function(check_flag result flag_name)
-  list(FIND ARGN ${flag_name}_FLAG has_flag)
+  list(FIND ARGN ${flag_name} has_flag)
   if(${has_flag} LESS 0)
-    list(FIND ARGN "${flag_name}_FLAG__ONLY" has_flag)
+    list(FIND ARGN "${flag_name}__ONLY" has_flag)
   endif()
   if(${has_flag} GREATER -1)
     set(${result} TRUE PARENT_SCOPE)