Change the now Deprecated TEST_BIG_ENDIAN to CMAKE_C_BYTE_ORDER (dotn…

…et#97426)

* Change TEST_BIG_ENDIAN for CMAKE_CXX_BYTE_ORDER, as the former is now deprecated.

* Changed to using CMAKE_C_BYTE_ORDER to determine endianness, rather
than setting its value directly.

src/mono/CMakeLists.txt

@@ -114,9 +114,7 @@ set(HAVE_MOVING_COLLECTOR 1)
 set(HAVE_CONC_GC_AS_DEFAULT 1)
 set(MONO_INSIDE_RUNTIME 1)
 
-TEST_BIG_ENDIAN(IS_BIG_ENDIAN)
-
-if(IS_BIG_ENDIAN)
+if(CMAKE_C_BYTE_ORDER STREQUAL "BIG_ENDIAN")
   set(TARGET_BYTE_ORDER G_BIG_ENDIAN)
 else()
   set(TARGET_BYTE_ORDER G_LITTLE_ENDIAN)