configure.ac: fix definition of NO_EXCEPTIONS_CXXFLAGS

[Akim Demaille]

commit 9589f4e9803f44efe780e0a8d4353466d4fbb15f
Author: Akim Demaille <address@hidden>
Date:   Sun Sep 9 11:51:49 2018 +0200

    configure.ac: fix definition of NO_EXCEPTIONS_CXXFLAGS
    
    * configure.ac: Always define it, not just when --enable-gcc-warnings
    is passed.

diff --git a/configure.ac b/configure.ac
index e5b89a27..cf4428d7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -52,6 +52,9 @@ AC_CONFIG_HEADERS([lib/config.h:lib/config.in.h])
 # Checks for the compiler.
 AC_PROG_CC_STDC
 AC_PROG_CXX
+AC_LANG_PUSH([C++])
+gl_WARN_ADD([-fno-exceptions], [NO_EXCEPTIONS_CXXFLAGS])
+AC_LANG_POP([C++])
 
 # Gnulib (early checks).
 gl_EARLY
@@ -153,12 +156,12 @@ if test "$enable_gcc_warnings" = yes; then
   # ... possiby in std=c++11 mode.
   gl_WARN_ADD([-Wno-zero-as-null-pointer-constant], [FLEX_SCANNER_CXXFLAGS])
   CXXFLAGS=$save_CXXFLAGS
-  gl_WARN_ADD([-fno-exceptions], [NO_EXCEPTIONS_CXXFLAGS])
   # Clang++ deprecates compiling C.
   gl_WARN_ADD([-Wno-deprecated], [WNO_DEPRECATED_CXXFLAGS])
   AC_LANG_POP([C++])
 fi
 
+
 BISON_TEST_FOR_WORKING_C_COMPILER
 BISON_C_COMPILER_POSIXLY_CORRECT
 BISON_TEST_FOR_WORKING_CXX_COMPILER