to avoid to conflict a env name

PKG_CONFIG_PATH is already used in pkg-config.

This fact induced a following problem on CentOS 5.8 for x86_64 architecture.

First, build libqrencode with "--libdir=/usr/local/lib64" option. Then, make and make install it. It deploys libqrencode.pc into /usr/local/lib64/pkgconfig.

Next, export PKG_CONFIG_PATH as "/usr/local/lib64/pkgconfig". Because, pkg-config on CentOS 5.8 not seen this path. ("/usr/local/lib/pkgconfig" not seen too).

Then, do "cpanm Text::QRCode". But, it was fail to make. Because, Makefile.PL execute $PKG_CONFIG_PATH as pkg-config.

A solution is to rename PKG_CONFIG_PATH of Makefile.PL.

Best regards.