configure: Use the environment variable CC when compiling tcc

Using the environment CC is a common used feature to
select a compiler to build any software,
so it should be supported when building tcc.

The old way using the parameter --cc still works.

Signed-off-by: Detlef Riekenberg <wine.dev@web.de>

configure

@@ -27,7 +27,8 @@ mandir=""
 infodir=""
 sysroot=""
 cross_prefix=""
-cc="gcc"
+test -z "$CC" && CC="gcc"
+test -z "$cc" && cc="$CC"
 ar="ar"
 bigendian="no"
 mingw32="no"
@@ -45,7 +46,7 @@ confvars=
 suggest="yes"
 gcc_major=0
 gcc_minor=0
-cc_name="gcc"
+cc_name="$cc"
 ar_set=
 darwin=
 cpu=