[CMake] Silence unused variable warning in compiler check

[phosek]

Summary

This is breaking the compiler check on bots.

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

 # If successful, saves target flags for this architecture.
 macro(test_target_arch arch def)
   string(RANDOM TARGET_${arch}_NAME)
   set(TARGET_${arch}_NAME "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/cmTC_${TARGET_${arch}_NAME}.dir")
   file(MAKE_DIRECTORY ${TARGET_${arch}_NAME})
   if(SANITIZER_CXX_ABI_INTREE)
     # We're using in tree C++ ABI, only test the C compiler for now.
     set(TARGET_${arch}_FILENAME "${TARGET_${arch}_NAME}/CheckTarget.c")
-    file(WRITE "${TARGET_${arch}_FILENAME}" "#include <stdlib.h>\nint main() { void *p = malloc(1); return 0; }\n")
+    file(WRITE "${TARGET_${arch}_FILENAME}" "#include <stdlib.h>\nint main() { (void)malloc(sizeof(int)); return 0; }\n")
   else()
     # We're using the system C++ ABI, test that we can build C++ programs.
     set(TARGET_${arch}_FILENAME "${TARGET_${arch}_NAME}/CheckTarget.cpp")
-    file(WRITE "${TARGET_${arch}_FILENAME}" "#include <new>\nint main() { int *p = new int; return 0; }\n")
+    file(WRITE "${TARGET_${arch}_FILENAME}" "#include <new>\nint main() { (void) new int; return 0; }\n")
   endif()
 
   set(TARGET_${arch}_CFLAGS ${ARGN})
   set(TARGET_${arch}_LINK_FLAGS ${ARGN})
   set(argstring "")
   foreach(arg ${ARGN})
     set(argstring "${argstring} ${arg}")
   endforeach()