Also build/install taglib.pc when targetting windows

.pc file is notably used when cross-compiling windows software
Changed XM::File::save() to use seek() properly.
Merge pull request #347 from TsudaKageyu/xm-seek

Changed XM::File::save() to use seek() properly.
Reduced a useless memory copy in tstring.cpp.
Fixed a typo in INSTALL.
Merge pull request #349 from TsudaKageyu/install-typo

Fixed a typo in INSTALL.
Merge pull request #348 from TsudaKageyu/string-memcpy

Reduced a useless memory copy in tstring.cpp.
Merge pull request #338 from funman/master

Also build/install taglib_c.pc when targetting windows
Merge remote-tracking branch 'upstream/master'