Support parallel make check with GNU make 4.2+

[Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE>]

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I noticed that make -jN check would run make check-single when using GNU
make 4.2.1.

In the end, it turned out that this is due to this change from the make
4.2 NEWS file:

* The amount of parallelism can be determined by querying MAKEFLAGS, even when
  the job server is enabled (previously MAKEFLAGS would always contain only
  "-j", with no number, when job server was enabled).

The fix is trivial: just accept an optional arg to -j in Makefile.in
(saw_dash_j).  Tested on i386-pc-solaris2.11 with just make and make
-j/-jN with both make 3.82 and 4.2.1.

Ok for master?

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University


2018-06-13  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* Makefile.in (saw_dash_j): Allow for GNU make 4.2+ passing -jN in
	MAKEFLAGS.


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# HG changeset patch
# Parent  c46bee26ae481e40fea09b4bbdb35731ff6b354c
Support parallel make check with GNU make 4.2+

diff --git a/gdb/testsuite/Makefile.in b/gdb/testsuite/Makefile.in
--- a/gdb/testsuite/Makefile.in
+++ b/gdb/testsuite/Makefile.in
@@ -140,7 +140,7 @@ installcheck:
 # See whether -j was given to make.  Either it was given with no
 # arguments, and appears as "j" in the first word, or it was given an
 # argument and appears as "-j" in a separate word.
-saw_dash_j = $(or $(findstring j,$(firstword $(MAKEFLAGS))),$(filter -j,$(MAKEFLAGS)))
+saw_dash_j = $(or $(findstring j,$(firstword $(MAKEFLAGS))),$(filter -j%,$(MAKEFLAGS)))
 
 # Try to run the tests in parallel if any -j option is given.  If RUNTESTFLAGS
 # is not empty, then by default the tests will be serialized.  This can be