Use -fno-show-column in libstdc++ installed testing

[Joseph Myers]

<https://gcc.gnu.org/ml/libstdc++/2016-08/msg00006.html> arranged for
libstdc++ tests to use -fno-show-column by default, but only for
build-tree testing.  This patch adds it to the options used for
installed testing as well.

Tested with installed testing for a cross to x86_64-linux-gnu, where
it fixes various test failures.

2018-10-02  Joseph Myers  <joseph@codesourcery.com>

	* testsuite/lib/libstdc++.exp (libstdc++_init): Use
	-fno-show-column in default cxxflags.

Index: libstdc++-v3/testsuite/lib/libstdc++.exp
===================================================================
--- libstdc++-v3/testsuite/lib/libstdc++.exp	(revision 264770)
+++ libstdc++-v3/testsuite/lib/libstdc++.exp	(working copy)
@@ -239,7 +239,7 @@ proc libstdc++_init { testfile } {
 
     # Default settings.
     set cxx [transform "g++"]
-    set cxxflags "-fmessage-length=0"
+    set cxxflags "-fmessage-length=0 -fno-show-column"
     set cxxpchflags ""
     set cxxvtvflags ""
     set cxxldflags ""

-- 
Joseph S. Myers
joseph@codesourcery.com