no-c++.m4: bug fix: egrep: repetition-operator operand invalid

[Sam Steingold]

Hi,

On Darwin (Mac OS) the gt_NO_CXX test fails because "Is g++" is not a
valid repetition-operator operand.

The attached patch fixes the problem.

>From d5d949b838c7cf4adb0e6e615795003ac7b0f1c3 Mon Sep 17 00:00:00 2001
From: Sam Steingold <address@hidden>
Date: Tue, 5 Dec 2017 11:02:33 -0500
Subject: [PATCH] Avoid the "egrep: repetition-operator operand invalid" error
 on Darwin

---
 m4/no-c++.m4 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/m4/no-c++.m4 b/m4/no-c++.m4
index ed06b22b6..b2fa0184f 100644
--- a/m4/no-c++.m4
+++ b/m4/no-c++.m4
@@ -7,14 +7,14 @@ dnl with or without modifications, as long as this notice is 
preserved.
 # Support for C source files that cannot be compiled by a C++ compiler.
 # Set NO_CXX to the C++ compiler flags needed to request C mode instead of
 # C++ mode.
-# So far only g++ is supported.
+# So far only g++ and clang++ are supported.
 
 AC_DEFUN([gt_NO_CXX],
 [
   NO_CXX=
-  AC_EGREP_CPP([Is g++], [
+  AC_EGREP_CPP([Is c plus plus], [
 #if defined __GNUC__ && defined __cplusplus
-  Is g++
+  Is c plus plus
 #endif
     ],
     [NO_CXX="-x c"])
-- 
2.15.1

Thanks.

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
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