Convert more .cvsignore files into gitignore files.

.gitignore:
    Ignore the generated file confdefs.h.

boehm_gc/.cvsignore:
boehm_gc/libatomic_ops/src/.cvsignore:
boehm_gc/libatomci_ops/src/.cvsignore:
    Convert to .gitignore files.

.gitignore

@@ -9,6 +9,7 @@ config.status
 config.log
 configure.log
 configure.help
+confdefs.h
 so_locations
 Mmake.common
 Mmake.params