Do not add $cross_prefix to compiler name given with --cc option

Originally committed as revision 15657 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -953,7 +953,7 @@ mandir_default='${prefix}/share/man'
 shlibdir_default="$libdir_default"
 
 # toolchain
-cc="gcc"
+cc_default="gcc"
 yasmexe="yasm"
 ar="ar"
 nm="nm"
@@ -1118,13 +1118,15 @@ disabled logging && logfile=/dev/null
 echo "# $0 $@" > $logfile
 set >> $logfile
 
-cc="${cross_prefix}${cc}"
+cc_default="${cross_prefix}${cc_default}"
 yasmexe="${cross_prefix}${yasmexe}"
 ar="${cross_prefix}${ar}"
 nm="${cross_prefix}${nm}"
 ranlib="${cross_prefix}${ranlib}"
 strip="${cross_prefix}${strip}"
 
+set_default cc
+
 # set temporary file name
 if test ! -z "$TMPDIR" ; then
     TMPDIR1="${TMPDIR}"