wayland.gyp: Use pkg-config-wrapper from the right location.

When |sysroot| is set (ie. one is building for ARM, for example),
instead of calling pkg-config directly gyp calls pkg-config-wrapper
instead. Refer to it in the right place: it is in src/build/linux, not
src/ozone/wayland.
Merge pull request #233 from rakuco/right-pkg-config-wrapper-location

wayland.gyp: Use pkg-config-wrapper from the right location.