More improvements for cygwin building

Removed more -fPIC for cygwin builds, included stuff from https://github.com/radare/radare2/pull/847

But! Installation still doesn't work properly:
```
 ~/radare/radare2
$ make install
/usr/bin/install -d /usr/local/share/doc/radare2
for a in doc/* ; do /usr/bin/install -m 644 $a /usr/local/share/doc/radare2 ; done
mkdir -p /usr/local/share/man/man1
for a in man/*.1 ; do /usr/bin/install -m 444 $a /usr/local/share/man/man1 ; done
cd /usr/local/share/man/man1 && ln -fs radare2.1 r2.1
rm -rf         @echo '/' | sed -e 's,//,/,g' -e 's,//,/,g' -e 's,/$,,'
rm: it is dangerous to operate recursively on `/'
rm: use --no-preserve-root to override this failsafe
rm -rf         @echo '//usr/local/lib' | sed -e 's,//,/,g' -e 's,//,/,g' -e 's,/$,,'/radare2/0.9.8.git/www # old dir
sed: -e expression #3, char 7: unknown option to `s'
Makefile:115: recipe for target 'install-www' failed
make: *** [install-www] Error 1
```