crt: Use headers: Use __SIZEOF_LONG_DOUBLE__ instead of arch checks in some math functions.

Signed-off-by: Jacek Caban <jacek@codeweavers.com>
diff --git a/mingw-w64-crt/math/frexpl.c b/mingw-w64-crt/math/frexpl.c
index f686a74..f60b68b 100644
--- a/mingw-w64-crt/math/frexpl.c
+++ b/mingw-w64-crt/math/frexpl.c
@@ -5,7 +5,7 @@
  */
 long double frexpl(long double value, int* exp);
 
-#if defined(_ARM_) || defined(__arm__) || defined(_ARM64_) || defined(__aarch64__)
+#if __SIZEOF_LONG_DOUBLE__ == __SIZEOF_DOUBLE__
 
 double frexp(double value, int* exp);