Always build tests if we enabled installed-tests

If we're cross-compiling, the installed-tests are useful even if we
can't run them on the build machine: we can copy them to the host
machine (possibly via a distro package like Debian's libglib2.0-tests)
and run them there.

While I'm changing the build-tests condition anyway, deduplicate it.

Based on a patch by Helmut Grohne.

Bug-Debian: https://bugs.debian.org/941509
Signed-off-by: Simon McVittie <smcv@collabora.com>

gio/meson.build

@@ -1009,8 +1009,6 @@ if enable_systemtap
 endif
 
 subdir('fam')
-# Don’t build the tests unless we can run them (either natively or in an exe wrapper)
-build_tests = not meson.is_cross_build() or (meson.is_cross_build() and meson.has_exe_wrapper())
 if build_tests
     subdir('tests')
 endif