C++ fix and test

[Pavel Roskin]

Hello!

This patch should close a long standing bug with C++. Also it adds the
first test involving a C++ compiler.

ChangeLog:
        * aclang.m4: (AC_LANG_SOURCE(C++)): Don't declare exit().
        Define it as a macro.
        * tests/compile.at: (AC_CHECK_LIB, C++): Test for AC_CHECK_LIB
        when the current language is C++.

Regards,
Pavel Roskin

_________________________________
Index: aclang.m4
--- aclang.m4
+++ aclang.m4
@@ -423,7 +423,8 @@
 [#line __oline__ "configure"
 #include "confdefs.h"
 #ifdef __cplusplus
-extern "C" void exit (int);
+#undef exit
+#define exit(x) return (x)
 #endif
 $1])

Index: tests/compile.at
--- tests/compile.at
+++ tests/compile.at
@@ -115,6 +115,24 @@



+## -------------- ##
+## C++ Compiler.  ##
+## -------------- ##
+
+
+# AC_CHECK_LIB, C++
+# -----------------
+# `cos' should be either in libc or in libm.
+# The compiler can issue warnings about `cos' being defined differently,
+# but configure should find it.
+AT_CHECK_MACRO([AC_CHECK_LIB, C++],
+[AC_LANG(C++)
+AC_TRY_LINK_FUNC(cos, [AS_EXIT(0)])
+AC_CHECK_LIB(m, cos,,
+             [AC_MSG_ERROR([cannot find `cos'])])])
+
+
+
 ## --------------------- ##
 ## Fortran 77 Compiler.  ##
 ## --------------------- ##
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