Makefile.in: Run the build directory goals serially (BZ 34699)

The builddir Makefile runs a separate make in the source directory
for each goal, so 'make -jN check xcheck' runs both at the same time.

Since a subdirectory's xtests also builds and runs its tests, the two
instances build the same targets concurrently and fail when renaming
the shared temporary files.

Add .NOTPARALLEL so the goals run one after another; each still builds
in parallel.

Checked on x86_64-linux-gnu.

Reviewed-by: Arjun Shankar <arjun@redhat.com>

Makefile.in

@@ -16,6 +16,8 @@ test-supported-fortify = @libc_cv_test_supported_fortify_source@
 
 .PHONY: all install bench
 
+.NOTPARALLEL:
+
 all .DEFAULT:
 	$(MAKE) -r PARALLELMFLAGS="$(PARALLELMFLAGS)" -C $(srcdir) objdir=`pwd` $@