preprocessor: Make quoting : [PR 95253]

[Nathan Sidwell]

I changed the quoting of ':', this restores it.  Make doesn't need ':' 
quoting (in a filename).

            PR preprocessor/95253
            libcpp/
            * mkdeps.c (munge): Do not escape ':'.
--
Nathan Sidwell
diff --git i/libcpp/mkdeps.c w/libcpp/mkdeps.c
index 471e449a19d..1867e0089d7 100644
--- i/libcpp/mkdeps.c
+++ w/libcpp/mkdeps.c
@@ -162,7 +162,6 @@ munge (const char *str, const char *trail = nullptr)
 	      /* FALLTHROUGH  */
 
 	    case '#':
-	    case ':':
 	      buf[dst++] = '\\';
 	      /* FALLTHROUGH  */