tweak compiler identification: check GNU compatibility first & then do ID checks.

config.h.in

@@ -88,7 +88,7 @@
 /* Define to 1 if you have the `fstatat' function. */
 #undef HAVE_FSTATAT
 
-/* Uses the GNU gcc compiler */
+/* Uses the GNU g++ compiler */
 #undef HAVE_GCC
 
 /* Define to 1 if you have the `getaddrinfo' function. */
@@ -109,6 +109,9 @@
 /* Define to 1 if you have the `getuid' function. */
 #undef HAVE_GETUID
 
+/* Compiler supports GNU C++ dialect & args */
+#undef HAVE_GNUC
+
 /* Define to 1 if you have the <grp.h> header file. */
 #undef HAVE_GRP_H
 
@@ -124,6 +127,9 @@
 /* Define to 1 if you have the <iconv.h> header file. */
 #undef HAVE_ICONV_H
 
+/* Uses the Intel ICC compiler */
+#undef HAVE_INTEL_ICC
+
 /* Define to 1 if you have the <inttypes.h> header file. */
 #undef HAVE_INTTYPES_H
 

configure

@@ -4143,7 +4143,7 @@ if test -z "$CXX"; then
     CXX=$CCC
   else
     if test -n "$ac_tool_prefix"; then
-  for ac_prog in g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icc owcc cl KCC cfront c++
+  for ac_prog in g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icpc owcc cl KCC cfront c++
   do
     # Extract the first word of "$ac_tool_prefix$ac_prog", so it can be a program name with args.
 set dummy $ac_tool_prefix$ac_prog; ac_word=$2
@@ -4187,7 +4187,7 @@ fi
 fi
 if test -z "$CXX"; then
   ac_ct_CXX=$CXX
-  for ac_prog in g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icc owcc cl KCC cfront c++
+  for ac_prog in g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icpc owcc cl KCC cfront c++
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
 set dummy $ac_prog; ac_word=$2
@@ -4869,15 +4869,34 @@ fi
 
 
 
-if test "x${CXX}" = "xg++"; then
+if test "x${GXX}" != "x"; then
-
-$as_echo "#define HAVE_GCC 1" >>confdefs.h
-
 
     CFLAGS=${CFLAGS:-"-O -pipe"}
     CXXFLAGS=${CXXFLAGS:-"-O -pipe"}
-fi
 
+
+$as_echo "#define HAVE_GNUC 1" >>confdefs.h
+
+
+    case "${CXX}" in
+        *clang++*)
+
+$as_echo "#define HAVE_CLANG 1" >>confdefs.h
+
+	    ;;
+	icpc)
+
+$as_echo "#define HAVE_INTEL_ICC 1" >>confdefs.h
+
+	    ;;
+	*)
+
+$as_echo "#define HAVE_GCC 1" >>confdefs.h
+
+	    ;;
+    esac
+
+else
         if test "x${CXX}" = "xclang++"; then
 
 $as_echo "#define HAVE_CLANG 1" >>confdefs.h
@@ -4923,6 +4942,9 @@ $as_echo "#define HAVE_HP_ACC 1" >>confdefs.h
     fi
 
 
+fi
+
+
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether C++ compiler accepts -Wall" >&5
 $as_echo_n "checking whether C++ compiler accepts -Wall... " >&6; }

configure.ac

@@ -29,7 +29,7 @@ dnl ###################
 dnl Checks for programs
 dnl ###################
 AC_PROG_CC([gcc clang suncc aCC xlc_r gxlc cl])
-AC_PROG_CXX([g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icc owcc cl KCC cfront c++])
+AC_PROG_CXX([g++ clang++ sunCC aCC xlc++_r gxlc++ ixlc icpc owcc cl KCC cfront c++])
 AC_PROG_RANLIB
 AC_PROG_YACC
 AC_PROG_LN_S
@@ -46,14 +46,30 @@ dnl #########################################
 dnl Set up per-compiler constants & base args
 dnl #########################################
 
-dnl if test "x${GXX}" != "x"; then
+dnl first look at compilers that define __GNUC__
-if test "x${CXX}" = "xg++"; then
+dnl since automake is good at that.
-    AC_DEFINE(HAVE_GCC, 1, [Uses the GNU gcc compiler])
+dnl
+if test "x${GXX}" != "x"; then
 
     CFLAGS=${CFLAGS:-"-O -pipe"}
     CXXFLAGS=${CXXFLAGS:-"-O -pipe"}
-fi
 
+    AC_DEFINE(HAVE_GNUC, 1, [Compiler supports GNU C++ dialect & args])
+    
+    case "${CXX}" in
+        *clang++*)
+            AC_DEFINE(HAVE_CLANG, 1, [Uses the Clang++ compiler])
+	    ;;
+	icpc)
+            AC_DEFINE(HAVE_INTEL_ICC, 1, [Uses the Intel ICC compiler])
+	    ;;	
+	*)
+            AC_DEFINE(HAVE_GCC, 1, [Uses the GNU g++ compiler])
+	    ;;	
+    esac
+
+else
+    dnl in case Clang stops defining __GNUC__ or user undefines it
     if test "x${CXX}" = "xclang++"; then
 	AC_DEFINE(HAVE_CLANG, 1, [Uses the Clang compiler])
 
@@ -91,6 +107,9 @@ if test "x${CXX}" = "xaCC"; then
         AC_DEFINE(HAVE_HP_ACC, 1, [Uses the aCC compiler])
     fi
  
+
+fi
+
 dnl ######################
 dnl Enable various warnings
 dnl #####################