tests: use correct pkg-config when cross compiling

By convention, the PKG_CONFIG environment variable is used to tell
build systems which pkg-config executable should be used.  This is
often used when cross compiling, where it might be set to something
like "aarch64-unknown-linux-gnu-pkg-config".

Signed-off-by: Alyssa Ross <hi@alyssa.is>
Message-ID: <20240123130409.181128-2-hi@alyssa.is>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -32,7 +32,7 @@ if [ -n "$NO_YAML" ]; then
         no_yaml=false
     fi
 else
-    if pkg-config --atleast-version 0.2.3 yaml-0.1; then
+    if ${PKG_CONFIG:-pkg-config} --atleast-version 0.2.3 yaml-0.1; then
         no_yaml=false
     else
         no_yaml=true