Makefile.in (SELFTEST_FLAGS): Use nul instead of /dev/null on mingw build hosts.

2017-11-28  Olivier Hainque  <hainque@adacore.com>

	* Makefile.in (SELFTEST_FLAGS): Use nul instead of /dev/null
	on mingw build hosts.

From-SVN: r255200

gcc/ChangeLog

+2017-11-28  Olivier Hainque  <hainque@adacore.com>
+
+	* Makefile.in (SELFTEST_FLAGS): Use nul instead of /dev/null
+	on mingw build hosts.
+
 2017-11-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR debug/81307

gcc/Makefile.in

@@ -1912,9 +1912,12 @@ rest.cross: specs
 # Specify -o /dev/null so the output of -S is discarded. More importantly
 # It does not try to create a file with the name "null.s" on POSIX and
 # "nul.s" on Windows. Because on Windows "nul" is a reserved file name.
+# Beware that /dev/null is not available to mingw tools, so directly use
+# "nul" instead of "/dev/null" if we're building on a mingw machine.
 # Specify the path to gcc/testsuite/selftests within the srcdir
 # as an argument to -fself-test.
-SELFTEST_FLAGS = -nostdinc /dev/null -S -o /dev/null \
+DEVNULL=$(if $(findstring mingw,$(build)),nul,/dev/null)
+SELFTEST_FLAGS = -nostdinc $(DEVNULL) -S -o $(DEVNULL) \
 	-fself-test=$(srcdir)/testsuite/selftests
 
 C_SELFTEST_FLAGS = -xc $(SELFTEST_FLAGS)