Filter out -fPIC too

...which happens to be passed in when building external/poppler with clang-cl

Change-Id: I2c17bec316081a0cdc789a84bb1447acf5e893c0

solenv/gcc-wrappers/wrapper.cxx

@@ -147,7 +147,7 @@ string processccargs(vector<string> rawargs) {
             // "foo.def" by itself
             linkargs.append(" " + *i);
         }
-        else if(!(*i).compare(0,12,"-fvisibility")) {
+        else if(!(*i).compare(0,12,"-fvisibility") || *i == "-fPIC") {
             //TODO: drop other gcc-specific options
         }
         else if(!(*i).compare(0,4,"-Wl,")) {