src/lib/gcrypt/meson.build: use dependency() for quering linker flags

Since version 0.49.0 the Meson build system has native support for
finding and using the gcrypt library using the `dependency()` function.

`dependency()` has the advantage over `find_library()` as it queries the
required linker flags for proper linking with external libraries, e.g.
libgpg-error.

As the latest released version 1.8.4 of libgcrypt does not
provide a .pc file, using `libgcrypt-config` is the only way to query
the required linker flags.

Unfortunately, there is an issue when cross compiling mpd and the user does not
define `libgcrypt-config` in the cross file. If the user sets the qobuz feature
to `auto` and the target does not have libgcrypt installed, the Meson
build system will falsly assume libgcrypt is available for the target as
it uses the native `libgcrypt-config` on the host and pretend is has
found the library.

Therefore, we still rely on `find_library()` to workaround this buggy
behavior. This way, if qobuz feature detection is set to `auto`, the
feature is disabled in case there is no target libgcrypt available.

Fixes building mpd statically with the qobuz feature enabled. Otherwise
the build fails with undefined references because of the missing libgpg-error
dependency:

```
/sysroot/usr/lib/libgcrypt.a(libgcrypt_la-visibility.o): In function `gcry_strerror':
visibility.c:(.text+0x14): undefined reference to `gpg_strerror'
```

1 files changed, 13 insertions, 0 deletions

diff --git a/src/lib/gcrypt/meson.build b/src/lib/gcrypt/meson.build
index 48297e279..5840bfe4d 100644
--- a/src/lib/gcrypt/meson.build
+++ b/src/lib/gcrypt/meson.build
@@ -1,4 +1,17 @@
+# Since version 0.49.0 Meson has native libgcrypt dependency support, which has
+# the advantage over find_library() as it uses libgcrypt-config to query the
+# required linker flags.
+# However, we still need to use find_library() first, to prevent Meson
+# falsly assuming a target libgcrypt is available in case there is no
+# libgcrypt-config entry in the cross file and libgcrypt is installed on the
+# host. In this case, Meson will falsly use the native libgcrypt-config and
+# will falsly assume it has found the gcrypt library for the target.
+#
+# See: https://github.com/MusicPlayerDaemon/MPD/pull/495
 gcrypt_dep = c_compiler.find_library('gcrypt', required: get_option('qobuz'))
+if gcrypt_dep.found()
+  gcrypt_dep = dependency('libgcrypt')
+endif
 if not gcrypt_dep.found()
   subdir_done()
 endif