improved compiler test.. works with icc 8.0

[[Imported from SVN: r964]]

m4/dune_compiler.m4

 # $Id$
-# check for gcc >= 3.4.1
+# check for supported compilers
 
 AC_DEFUN([DUNE_CHECK_COMPILER],[
+
+AC_ARG_ENABLE(compilercheck,
+  AC_HELP_STRING([--enable-compilercheck],
+                 [check for supported compilers \[default=yes\]]),
+  [compilercheck=$enable],
+  [compilercheck=yes]
+)
+
+SUPPORTED_COMPILER="gcc (>= 3.4.1) or icc (>= 7.0)"
+
 AC_REQUIRE([AC_PROG_CXX])
 cat >conftest.cc <<_ACEOF
+#ifdef __ICC
+  #if __ICC >= 700
+    #define CXX_SUPPORTED
+  #endif
+#endif
 #ifdef __GNUC__
-#if __GNUC__ > 3 || \
-   (__GNUC__ == 3 && (__GNUC_MINOR__ > 4 || \
-      (__GNUC_MINOR__ == 4 && \
-       __GNUC_PATCHLEVEL__ >= 1)))
-#else
-#error You need gcc version >= 3.4.1
+  #if __GNUC__ > 3 || \
+     (__GNUC__ == 3 && (__GNUC_MINOR__ > 4 || \
+        (__GNUC_MINOR__ == 4 && \
+         __GNUC_PATCHLEVEL__ >= 1)))
+    #define CXX_SUPPORTED
+  #endif
 #endif
+#ifndef CXX_SUPPORTED
+  #error Your compiler is not officially supprted by dune
 #endif
 int main() { return 0; }
 _ACEOF
-if $CXX conftest.cc -o conftest.$ac_exeext >&5; then
-  rm -f conftest.$ac_exeext
+
+if test "x$compilercheck" != "xyes" ; then
+  AC_MSG_WARN([compilercheck is disabled. DANGEROUS!])    
 else
-  AC_MSG_ERROR([When using gcc, you need gcc-version >= 3.4.1])    
+  if $CXX conftest.cc -o conftest.$ac_exeext >&5; then
+    rm -f conftest.$ac_exeext
+  else
+    AC_MSG_ERROR([Your compiler is not officially supported by dune
+                  dune is known to work with $SUPPORTED_COMPILER])
+  fi
 fi
-])
\ No newline at end of file
+
+])