ARMCC: Fix identification of ARM compiler when it defines GNU macros

According to ARMCC 5.06 documentation:

    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0472m/chr1359125007083.html

the compiler may define `__GNUC__` in addition to `__ARMCC_VERSION`.
Re-order our preprocessor checks to consider the ARM-specific macro
first so that the ARM compiler is not mistaken for a GNU compiler.

Fixes: #19065

Modules/CMakeCompilerIdDetection.cmake

@@ -73,13 +73,13 @@ function(compiler_id_detection outvar lang)
     endif()
     list(APPEND ordered_compilers
       SCO
+      ARMCC
       AppleClang
       Clang
       GNU
       MSVC
       ADSP
       IAR
-      ARMCC
     )
     if (lang STREQUAL C)
       list(APPEND ordered_compilers