FindPkgConfig: return actual error when a package is not found (#15810)

In some cases, CMake returned the following error:

-- Checking for module 'foo'
--   Package 'foo' not found

When the actual error returned by pkg-config was:

  Package 'bar', required by 'foo', not found

Now, the actual error is forwarded to the user.

-- Checking for module 'foo'
--   Package 'bar', required by 'foo', not found

For the standard case (i.e. the package was indeed not found), the
CMake error was:

-- Checking for module 'foo'
--   Package 'foo' not found

But it now prints:

-- Checking for module 'foo'
--   No package 'foo' found

The associated test was also updated. ${last} refers to the last
CLI argument.

1 files changed, 3 insertions, 2 deletions

diff --git a/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh b/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh
index 852e841..abe14bf 100755
--- a/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh
+++ b/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh
@@ -10,9 +10,10 @@ case $1 in
     ;;
   --exists)
     shift
-    echo "Expected: $@"
+    eval last=\${$#}
+    echo "Expected: ${last}"
     echo "Found:    ${PKG_CONFIG_PATH}"
-    [ "$@" = "${PKG_CONFIG_PATH}" ] || exit 1
+    [ "${last}" = "${PKG_CONFIG_PATH}" ] || exit 1
     ;;
   *)
     exit 255