Avoid trying to include <asm/atomic.h> when it doesn't work in C++

code. (Bug #13621)


configure.in:
  Test whether atomic_add() and atomic_sub() are available in C++
  code, since that is primarily where we will be using them.

configure.in

@@ -830,6 +830,9 @@ AC_SUBST(WRAPLIBS)
 if test "$IS_LINUX" = "true"; then
   AC_MSG_CHECKING([for atomic operations])
 
+  AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+
   atom_ops=
   AC_TRY_RUN([
 #include <asm/atomic.h>
@@ -859,6 +862,8 @@ int main()
   if test -z "$atom_ops"; then atom_ops="no"; fi
   AC_MSG_RESULT($atom_ops)
 
+  AC_LANG_RESTORE
+
   AC_ARG_WITH(pstack,
     [  --with-pstack           Use the pstack backtrace library],
     [ USE_PSTACK=$withval ],