check if specified compiler exists

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@1826 c046a42c-6fe2-441c-8c8c-71466251a162

configure

@@ -283,6 +283,11 @@ cc="${cross_prefix}${cc}"
 ar="${cross_prefix}${ar}"
 strip="${cross_prefix}${strip}"
 
+if [ -z `which $cc` ] ; then
+    echo "Compiler $cc could not be found"
+    exit
+fi
+
 if test "$mingw32" = "yes" ; then
     linux="no"
     EXESUF=".exe"