Adjust modulemap to mark mm3dnow as textual header. (#107155)

This avoids issuing the deprecation diagnostic when building the module.

Not building it into a module shouldn't cause any negative impacts,
since it no longer has any declarations other than the header guard.
It's also very rarely included by anything.

Addresses
#96246 (comment)

clang/lib/Headers/module.modulemap

@@ -66,6 +66,8 @@ module _Builtin_intrinsics [system] [extern_c] {
     textual header "__wmmintrin_aes.h"
     textual header "__wmmintrin_pclmul.h"
 
+    textual header "mm3dnow.h"
+
     explicit module mm_malloc {
       requires !freestanding
       header "mm_malloc.h"
@@ -122,10 +124,6 @@ module _Builtin_intrinsics [system] [extern_c] {
       header "popcntintrin.h"
     }
 
-    explicit module mm3dnow {
-      header "mm3dnow.h"
-    }
-
     explicit module aes_pclmul {
       header "wmmintrin.h"
       export aes