[libc] Add -Wall for libc tests (#160220)

Relates to #119281

Author: vinay-deshmukh

libc/cmake/modules/LLVMLibCTestRules.cmake

@@ -39,7 +39,7 @@ function(_get_common_test_compile_options output_var c_test flags)
       list(APPEND compile_options "-ffixed-point")
     endif()
 
-    # list(APPEND compile_options "-Wall")
+    list(APPEND compile_options "-Wall")
     list(APPEND compile_options "-Wextra")
     # -DLIBC_WNO_ERROR=ON if you can't build cleanly with -Werror.
     if(NOT LIBC_WNO_ERROR)