meson: Fix Gd install location

Install the Gd library in libdir, instead of datadir.

Closes #159
3 jobs for wip/mschraal/meson-libdir-fix in 19 minutes and 10 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Check
passed #11840
pep8

00:06:46

passed #11839
pyflakes

00:06:45

 
  Build
passed #11841
build

00:12:23