(install-headers, install-headers-tar): Correctly handle directories

when $(libsubdir) is a relative path.

From-SVN: r6259

gcc/Makefile.in

@@ -1939,15 +1939,15 @@ install-include-dir: install-dir
 
 # Install the include directory using tar.
 install-headers-tar: stmp-headers $(STMP_FIXPROTO) install-include-dir
-	cd include; \
-	 (tar cf - .; exit 0) | (cd $(libsubdir)/include; tar $(TAROUTOPTS) - )
+	(cd include; \
+	 tar cf - .; exit 0) | (cd $(libsubdir)/include; tar $(TAROUTOPTS) - )
 # /bin/sh on some systems returns the status of the first tar,
 # and that can lose with GNU tar which always writes a full block.
 # So use `exit 0' to ignore its exit status.
 
 # Install the include directory using cpio.
 install-headers-cpio: stmp-headers $(STMP_FIXPROTO) install-include-dir
-	cd include; find . -print | cpio -pdum $(libsubdir)/include
+	(cd include; find . -print) | cpio -pdum $(libsubdir)/include
 
 # Put assert.h where it won't override GNU libc's assert.h.
 # It goes in a dir that is searched after GNU libc's headers;