Fix dependency generation with ccache/gcc

When running behind ccache, the output from -MMD is corrupted unless
we also use the -MF and -MT flags.

Since ccache is difficult to detect and gcc 2.x doesn't support the
-MF and -MT flags, we always use the old dependency generation method
when gcc 2.x is detected.

Originally committed as revision 19620 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1510,8 +1510,10 @@ filter_asflags=echo
 
 if   $cc -v 2>&1 | grep -qi ^gcc; then
     cc_type=gcc
-    CC_DEPFLAGS='-MMD'
-    AS_DEPFLAGS='-MMD'
+    if ! $cc -dumpversion | grep -q '^2\.'; then
+        CC_DEPFLAGS='-MMD -MF $(@:.o=.d) -MT $@'
+        AS_DEPFLAGS='-MMD -MF $(@:.o=.d) -MT $@'
+    fi
 elif $cc --version 2>/dev/null | grep -q Intel; then
     cc_type=icc
     CC_DEPFLAGS='-MMD'