[compiler-rt] Use arm-specific builtins sources for arm/mingw builds

Previously, that configuration only used the generic sources, in
addition to the couple specifically chosen arm/mingw files.

Differential Revision: https://reviews.llvm.org/D98547

compiler-rt/lib/builtins/CMakeLists.txt

@@ -489,7 +489,7 @@ if(MINGW)
     arm/aeabi_uldivmod.S
     arm/chkstk.S
     mingw_fixfloat.c
-    ${GENERIC_SOURCES}
+    ${arm_SOURCES}
   )
 elseif(NOT WIN32)
   # TODO the EABI sources should only be added to EABI targets