Remove *.stderr when "make clean".

gold/
	* testsuite/Makefile.am (MOSTLYCLEANFILES): Add *.stderr.
	* testsuite/Makefile.in: Regenerate.

gold/ChangeLog

@@ -1,3 +1,8 @@
+2018-06-19  Cary Coutant  <ccoutant@gmail.com>
+
+	* testsuite/Makefile.am (MOSTLYCLEANFILES): Add *.stderr.
+	* testsuite/Makefile.in: Regenerate.
+
 2018-06-19  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* configure.ac: Remove AC_PREREQ, add missing quoting and usage

gold/testsuite/Makefile.am

@@ -81,7 +81,7 @@ endif
 # .o's), but not all of them (such as .so's and .err files).  We
 # improve on that here.  automake-1.9 info docs say "mostlyclean" is
 # the right choice for files 'make' builds that people rebuild.
-MOSTLYCLEANFILES = *.so *.syms *.stdout
+MOSTLYCLEANFILES = *.so *.syms *.stdout *.stderr
 
 # Export make variables to the shell scripts so that they can see
 # (for example) DEFAULT_TARGET.

gold/testsuite/Makefile.in

@@ -3075,7 +3075,7 @@ TEST_AS = $(top_builddir)/../gas/as-new
 # .o's), but not all of them (such as .so's and .err files).  We
 # improve on that here.  automake-1.9 info docs say "mostlyclean" is
 # the right choice for files 'make' builds that people rebuild.
-MOSTLYCLEANFILES = *.so *.syms *.stdout $(am__append_4) \
+MOSTLYCLEANFILES = *.so *.syms *.stdout *.stderr $(am__append_4) \
 	$(am__append_17) $(am__append_21) $(am__append_31) \
 	$(am__append_34) $(am__append_37) $(am__append_41) \
 	$(am__append_47) $(am__append_51) $(am__append_52) \