configure: do not rely on pathsearch if full executable path provided.

This issue was pointed out by Mark Callaghan. Fixes #90.

configure

@@ -561,10 +561,12 @@ else
 fi
 
 printf "Finding suitable compiler........"
+if test ! -x "${CC}"; then
 	CC=`pathsearch "${CC:-cc}"`
 	if test -z "$CC" -o ! -x "$CC"; then
 		CC=`pathsearch "${CC:-gcc}"`
 	fi
+fi
 assert "$CC" "not found"
 
 cat << EOF > .1.c
@@ -596,7 +598,7 @@ int main(void) {
 EOF
 
 $CC -o .1 .1.c
-COMPILER=`./.1`
+COMPILER=`./.1 2> /dev/null`
 r=$?
 rm -f .1.c .1