[libc] Pass through LIBC_CONF_MATH_OPTIMIZATIONS correctly (#113540)

It's checked in a cmake function that builds up a list called `config_options`. But the check was appending to a list called `compile_options`, so the intended `-DLIBC_MATH=whatever` didn't end up on the actual compile command lines.

Author: statham-arm

libc/cmake/modules/LLVMLibCCompileOptionRules.cmake

@@ -84,7 +84,7 @@ function(_get_compile_options_from_config output_var)
  endif()
 
  if(LIBC_CONF_MATH_OPTIMIZATIONS)
- list(APPEND compile_options "-DLIBC_MATH=${LIBC_CONF_MATH_OPTIMIZATIONS}")
+ list(APPEND config_options "-DLIBC_MATH=${LIBC_CONF_MATH_OPTIMIZATIONS}")
  endif()
 
  set(${output_var} ${config_options} PARENT_SCOPE)