CheckTypeSize: Avoid if() auto-dereferene in quoted arguments (#15571)

Exposed by a CMP0054 warning.  Set CMP0054 to NEW since no code in this
module depends on the old behavior.

Modules/CheckTypeSize.cmake

@@ -83,6 +83,7 @@ include(CheckIncludeFileCXX)
 
 cmake_policy(PUSH)
 cmake_policy(VERSION 3.0)
+cmake_policy(SET CMP0054 NEW)
 
 get_filename_component(__check_type_size_dir "${CMAKE_CURRENT_LIST_FILE}" PATH)
 
@@ -112,9 +113,9 @@ function(__check_type_size_impl type var map builtin language)
 
   # Perform the check.
 
-  if("${language}" STREQUAL "C")
+  if(language STREQUAL "C")
     set(src ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CheckTypeSize/${var}.c)
-  elseif("${language}" STREQUAL "CXX")
+  elseif(language STREQUAL "CXX")
     set(src ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CheckTypeSize/${var}.cpp)
   else()
     message(FATAL_ERROR "Unknown language:\n  ${language}\nSupported languages: C, CXX.\n")
@@ -229,11 +230,11 @@ macro(CHECK_TYPE_SIZE TYPE VARIABLE)
     set(_builtin 0)
   else()
     set(_builtin 1)
-    if("${_language}" STREQUAL "C")
+    if(_language STREQUAL "C")
       check_include_file(sys/types.h HAVE_SYS_TYPES_H)
       check_include_file(stdint.h HAVE_STDINT_H)
       check_include_file(stddef.h HAVE_STDDEF_H)
-    elseif("${_language}" STREQUAL "CXX")
+    elseif(_language STREQUAL "CXX")
       check_include_file_cxx(sys/types.h HAVE_SYS_TYPES_H)
       check_include_file_cxx(stdint.h HAVE_STDINT_H)
       check_include_file_cxx(stddef.h HAVE_STDDEF_H)