revert the --enable-clang option

This should be completely equivalent to ./autogen.sh CC=clang CXX=clang++ ,
which is the normal way to pass any compiler to configure, so this is needless
duplication.
This reverts commits 1a843cc5 and
02ed2608 .

Change-Id: Ib02ab84a7b84fe4797dca0f62aa5049c1be55302

configure.ac

@@ -1158,11 +1158,6 @@ AC_ARG_ENABLE(winegcc,
          needed for MinGW cross-compilation.]),
 )
 
-AC_ARG_ENABLE(clang,
-    AS_HELP_STRING([--enable-clang],
-        [Build using the clang compiler.]),
-)
-
 AC_ARG_ENABLE(liblangtag,
     AS_HELP_STRING([--disable-liblangtag],
         [Disable use of liblangtag, and insted use an own simple
@@ -2276,37 +2271,44 @@ if test "$CCACHE" != ""; then
     fi
 fi
 
-dnl ===================================================================
-dnl  Checks for Icecream
-dnl ===================================================================
-if test "$enable_icecream" = "yes"; then
-    if test -d "/usr/lib/icecc/bin"; then
-        ICECREAM_HOME="/usr/lib/icecc"
-    else
-        ICECREAM_HOME="/opt/icecream"
-    fi
-    if test -z "$CC"; then
-    	CC="$ICECREAM_HOME/bin/gcc"
-    fi
-    if test -z "$CXX"; then
-    	CXX="$ICECREAM_HOME/bin/g++"
-    fi
-fi
-
 dnl ===================================================================
 dnl  Checks for C compiler,
-dnl  AC_PROG_CC checks for gcc, cc and then cl (if it weren't guarded for win32)
 dnl  The check for the C++ compiler is later on.
 dnl ===================================================================
+if test "$_os" != "WINNT" -a "$WITH_MINGW" != "yes"; then
+	GCC_HOME_SET="true"
+	AC_MSG_CHECKING([gcc home])
+	if test -z "$with_gcc_home"; then
+		if test "$enable_icecream" = "yes"; then
+			if test -d "/usr/lib/icecc/bin"; then
+				GCC_HOME="/usr/lib/icecc/"
+			else
+				GCC_HOME="/opt/icecream/"
+			fi
+		else
+			GCC_HOME=`which gcc | $SED -e s,/bin/gcc,,`
+			GCC_HOME_SET="false"
+		fi
+	else
+		GCC_HOME="$with_gcc_home"
+	fi
+	AC_MSG_RESULT($GCC_HOME)
+	AC_SUBST(GCC_HOME)
+
+	if test "$GCC_HOME_SET" = "true"; then
+		if test -z "$CC"; then
+			CC="$GCC_HOME/bin/gcc"
+		fi
+		if test -z "$CXX"; then
+			CXX="$GCC_HOME/bin/g++"
+		fi
+	fi
+fi
+
+dnl The following checks for gcc, cc and then cl (if it weren't guarded for win32)
 if test "$_os" != "WINNT" -o "$WITH_MINGW" = "yes"; then
     # AC_PROG_CC sets CFLAGS to -g -O2 if not set, avoid that
     save_CFLAGS=$CFLAGS
-    if test "$enable_clang" = "yes"; then
-        AC_PATH_PROG(CC,clang)
-        if test -z "$CC"; then
-            AC_MSG_ERROR([Clang not found in path. Is it installed?])
-        fi
-    fi
     AC_PROG_CC
     CFLAGS=$save_CFLAGS
 fi
@@ -4998,12 +5000,6 @@ dnl ===================================================================
 if test "$_os" != "WINNT" -o "$WITH_MINGW" = "yes"; then
     # AC_PROG_CXX sets CXXFLAGS to -g -O2 if not set, avoid that
     save_CXXFLAGS=$CXXFLAGS
-    if test "$enable_clang" = "yes"; then
-        AC_PATH_PROG(CXX,clang++)
-        if test -z "$CXX"; then
-            AC_MSG_ERROR([clang++ not found in path. Is it installed?])
-        fi
-    fi
     AC_PROG_CXX
     CXXFLAGS=$save_CXXFLAGS
 else