Use the C++ compiler for feature tests

Most of the configure test results will be used in C++ sources, so testing for
them with the C compiler might give wrong results.

I had to fix a few standard tests to work with the C++ compiler. There are
still a small number of tests that require the C compiler and should not be
checked with the C++ compiler. They either check features of the C compiler
or their results will only be used in C source files (by the C compiler).

This should fix issue #1572

acinclude.m4

@@ -488,7 +488,7 @@ AC_DEFUN([MULE_CHECK_BFD],
 				#include <ansidecl.h>
 				#include <bfd.h>
 			]], [[
-				char *dummy = bfd_errmsg(bfd_get_error());
+				const char *dummy = bfd_errmsg(bfd_get_error());
 			]])
 		], [
 			result=yes
@@ -605,8 +605,8 @@ AC_DEFUN([MULE_CHECK_EXECINFO],
 			#include <execinfo.h>
 		]], [[
 			void *bt[1];
-			int n = backtrace(&bt, 1);
-			const char **bt_syms = backtrace_symbols(bt, n);
+			int n = backtrace((void **)&bt, 1);
+			char **bt_syms = backtrace_symbols(bt, n);
 		]])
 	], [
 		AH_TEMPLATE([HAVE_EXECINFO], [Define to 1 if you have the <execinfo.h> header which declares backtrace()])
@@ -617,6 +617,163 @@ AC_DEFUN([MULE_CHECK_EXECINFO],
 	])
 ])
 
+
+dnl ---------------------------------------------------------------------------
+dnl MULE_FUNC_MMAP
+dnl
+dnl This function is copied over from autoconf sources, but fixed to work with
+dnl C++.
+dnl ---------------------------------------------------------------------------
+AC_DEFUN([MULE_FUNC_MMAP],
+[AC_CHECK_HEADERS_ONCE([stdlib.h unistd.h sys/param.h])
+AC_CHECK_FUNCS([getpagesize])
+AC_CACHE_CHECK([for working mmap], [ac_cv_func_mmap_fixed_mapped],
+[AC_RUN_IFELSE([AC_LANG_SOURCE([AC_INCLUDES_DEFAULT]
+[[/* malloc might have been renamed as rpl_malloc. */
+#undef malloc
+
+/* Thanks to Mike Haertel and Jim Avera for this test.
+   Here is a matrix of mmap possibilities:
+	mmap private not fixed
+	mmap private fixed at somewhere currently unmapped
+	mmap private fixed at somewhere already mapped
+	mmap shared not fixed
+	mmap shared fixed at somewhere currently unmapped
+	mmap shared fixed at somewhere already mapped
+   For private mappings, we should verify that changes cannot be read()
+   back from the file, nor mmap's back from the file at a different
+   address.  (There have been systems where private was not correctly
+   implemented like the infamous i386 svr4.0, and systems where the
+   VM page cache was not coherent with the file system buffer cache
+   like early versions of FreeBSD and possibly contemporary NetBSD.)
+   For shared mappings, we should conversely verify that changes get
+   propagated back to all the places they're supposed to be.
+
+   Grep wants private fixed already mapped.
+   The main things grep needs to know about mmap are:
+   * does it exist and is it safe to write into the mmap'd area
+   * how to use it (BSD variants)  */
+
+#include <fcntl.h>
+#include <sys/mman.h>
+
+#if !defined STDC_HEADERS && !defined HAVE_STDLIB_H
+char *malloc ();
+#endif
+
+/* This mess was copied from the GNU getpagesize.h.  */
+#ifndef HAVE_GETPAGESIZE
+# ifdef _SC_PAGESIZE
+#  define getpagesize() sysconf(_SC_PAGESIZE)
+# else /* no _SC_PAGESIZE */
+#  ifdef HAVE_SYS_PARAM_H
+#   include <sys/param.h>
+#   ifdef EXEC_PAGESIZE
+#    define getpagesize() EXEC_PAGESIZE
+#   else /* no EXEC_PAGESIZE */
+#    ifdef NBPG
+#     define getpagesize() NBPG * CLSIZE
+#     ifndef CLSIZE
+#      define CLSIZE 1
+#     endif /* no CLSIZE */
+#    else /* no NBPG */
+#     ifdef NBPC
+#      define getpagesize() NBPC
+#     else /* no NBPC */
+#      ifdef PAGESIZE
+#       define getpagesize() PAGESIZE
+#      endif /* PAGESIZE */
+#     endif /* no NBPC */
+#    endif /* no NBPG */
+#   endif /* no EXEC_PAGESIZE */
+#  else /* no HAVE_SYS_PARAM_H */
+#   define getpagesize() 8192	/* punt totally */
+#  endif /* no HAVE_SYS_PARAM_H */
+# endif /* no _SC_PAGESIZE */
+
+#endif /* no HAVE_GETPAGESIZE */
+
+int
+main ()
+{
+  char *data, *data2, *data3;
+  int i, pagesize;
+  int fd, fd2;
+
+  pagesize = getpagesize ();
+
+  /* First, make a file with some known garbage in it. */
+  data = (char *) malloc (pagesize);
+  if (!data)
+    return 1;
+  for (i = 0; i < pagesize; ++i)
+    *(data + i) = rand ();
+  umask (0);
+  fd = creat ("conftest.mmap", 0600);
+  if (fd < 0)
+    return 2;
+  if (write (fd, data, pagesize) != pagesize)
+    return 3;
+  close (fd);
+
+  /* Next, check that the tail of a page is zero-filled.  File must have
+     non-zero length, otherwise we risk SIGBUS for entire page.  */
+  fd2 = open ("conftest.txt", O_RDWR | O_CREAT | O_TRUNC, 0600);
+  if (fd2 < 0)
+    return 4;
+  data2 = (char *) "";
+  if (write (fd2, data2, 1) != 1)
+    return 5;
+  data2 = (char *) mmap (0, pagesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd2, 0L);
+  if (data2 == MAP_FAILED)
+    return 6;
+  for (i = 0; i < pagesize; ++i)
+    if (*(data2 + i))
+      return 7;
+  close (fd2);
+  if (munmap (data2, pagesize))
+    return 8;
+
+  /* Next, try to mmap the file at a fixed address which already has
+     something else allocated at it.  If we can, also make sure that
+     we see the same garbage.  */
+  fd = open ("conftest.mmap", O_RDWR);
+  if (fd < 0)
+    return 9;
+  if (data2 != mmap (data2, pagesize, PROT_READ | PROT_WRITE,
+		     MAP_PRIVATE | MAP_FIXED, fd, 0L))
+    return 10;
+  for (i = 0; i < pagesize; ++i)
+    if (*(data + i) != *(data2 + i))
+      return 11;
+
+  /* Finally, make sure that changes to the mapped area do not
+     percolate back to the file as seen by read().  (This is a bug on
+     some variants of i386 svr4.0.)  */
+  for (i = 0; i < pagesize; ++i)
+    *(data2 + i) = *(data2 + i) + 1;
+  data3 = (char *) malloc (pagesize);
+  if (!data3)
+    return 12;
+  if (read (fd, data3, pagesize) != pagesize)
+    return 13;
+  for (i = 0; i < pagesize; ++i)
+    if (*(data + i) != *(data3 + i))
+      return 14;
+  close (fd);
+  return 0;
+}]])],
+	       [ac_cv_func_mmap_fixed_mapped=yes],
+	       [ac_cv_func_mmap_fixed_mapped=no],
+	       [ac_cv_func_mmap_fixed_mapped=no])])
+if test $ac_cv_func_mmap_fixed_mapped = yes; then
+  AC_DEFINE([HAVE_MMAP], [1],
+	    [Define to 1 if you have a working `mmap' system call.])
+fi
+rm -f conftest.mmap conftest.txt
+])
+
+
 dnl ---------------------------------------------------------------------------
 dnl MULE_CHECK_MMAP
 dnl
@@ -628,7 +785,7 @@ AC_DEFUN([MULE_CHECK_MMAP],
 
 	MULE_IF_ENABLED([mmap], [
 		AC_CHECK_HEADERS([sys/mman.h])
-		AC_FUNC_MMAP
+		MULE_FUNC_MMAP
 		AC_CHECK_FUNCS([munmap sysconf])
 		AS_IF([test $ac_cv_func_sysconf = yes], [
 			AC_MSG_CHECKING([for pagesize constant for sysconf])