FindPkgConfig: Extend PKG_CONFIG_PATH using CMake variables (#12926)

Use CMAKE_PREFIX_PATH, CMAKE_FRAMEWORK_PATH, and CMAKE_APPBUNDLE_PATH
cache and environment variables to extend PKG_CONFIG_PATH before calling
pkg-config.

In each of the path in these variables it searches for lib/pkgconfig.
Then, depending on the system, it searches for
lib/${CMAKE_LIBRARY_ARCHITECTURE}/pkgconfig (debian) or for
lib64/pkgconfig (other 64 bit unixes). If any of these path is found,
it is appended to the PKG_CONFIG_PATH enviromnent variable.

Add two new arguments to the pkg_check_module and pkg_search_module
macro, NO_CMAKE_PATH and NO_CMAKE_ENVIRONMENT_PATH. The new signature
are therefore:

   pkg_check_modules(<PREFIX> [REQUIRED] [QUIET]
                     [NO_CMAKE_PATH] [NO_CMAKE_ENVIRONMENT_PATH]
                     <MODULE> [<MODULE>]*)
   pkg_search_module(<PREFIX> [REQUIRED] [QUIET]
                     [NO_CMAKE_PATH] [NO_CMAKE_ENVIRONMENT_PATH]
                     <MODULE> [<MODULE>]*)

By default, if CMAKE_MINIMUM_REQUIRED_VERSION is 3.1 or later (in
order to keep compatibility with the previous behavior), or if
PKG_CONFIG_USE_CMAKE_PREFIX_PATH is set, the CMAKE_PREFIX_PATH,
CMAKE_FRAMEWORK_PATH, and CMAKE_APPBUNDLE_PATH cache and environment
variables will be added to pkgconfig search path.

The NO_CMAKE_PATH and NO_CMAKE_ENVIRONMENT_PATH arguments disable this
behavior for the cache variables and the environment variables,
respectively, similarly to the find_package() command.

1 files changed, 20 insertions, 0 deletions

diff --git a/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh b/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh
new file mode 100755
index 0000000..e62bb74
--- /dev/null
+++ b/Tests/RunCMake/FindPkgConfig/dummy-pkg-config.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# This is a replacement for pkg-config that compares the string passed
+# to the --exists argument with the PKG_CONFIG_PATH environment variable
+# and returns 1 if they are different.
+
+case $1 in
+  --version)
+    echo "0.0-cmake-dummy"
+    ;;
+  --exists)
+    shift
+    echo "$@"
+    echo "${PKG_CONFIG_PATH}"
+    [ "$@" = "${PKG_CONFIG_PATH}" ] || exit 1
+    ;;
+  *)
+    exit 255
+    ;;
+esac