Implement a workaround for GNU mak jobserver

Compiling binutils using -flto=jobserver with GCC 11 leads to

libtool: link: gcc -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Wstack-usage=262144 -Wwrite-strings -I../../gas/../zlib -g -O2 -fprofile-generate -flto=jobserver -o as-new app.o as.o atof-generic.o compress-debug.o cond.o depend.o dwarf2dbg.o dw2gencfi.o ecoff.o ehopt.o expr.o flonum-copy.o flonum-konst.o flonum-mult.o frags.o hash.o input-file.o input-scrub.o listing.o literal.o macro.o messages.o output-file.o read.o remap.o sb.o stabs.o subsegs.o symbols.o write.o config/tc-i386.o config/obj-elf.o config/atof-ieee.o  ../opcodes/.libs/libopcodes.a ../bfd/.libs/libbfd.a -L/tmp/binutils-gdb/objdir/zlib -lz ../libiberty/libiberty.a -ldl
lto-wrapper: warning: jobserver is not available: '--jobserver-auth=' is not present in 'MAKEFLAGS'

since the '+' is missing on the recipe line in Makefiles generated by
automake.  Add the '+' to the recipe line by hand.

bfd/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

binutils/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

config/

	PR binutils/26792
	* jobserver.m4: New file.

gas/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

gprof/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

ld/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

libctf/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

opcodes/

	PR binutils/26792
	* configure.ac: Use GNU_MAKE_JOBSERVER.
	* aclocal.m4: Regenerated.
	* configure: Likewise.

ld/configure.ac

@@ -597,3 +597,5 @@ AC_SUBST(pdfdir)
 
 AC_CONFIG_FILES(Makefile po/Makefile.in:po/Make-in)
 AC_OUTPUT
+
+GNU_MAKE_JOBSERVER