Fix pkg-config generation with absolute install dirs

Analogous to KhronosGroup/SPIRV-Tools#6483
Signed-off-by: Marcin Serwin <[email protected]>

Author: marcin-serwin

cmake/shaderc.pc.in

@@ -1,7 +1,7 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
-libdir=${prefix}/@CMAKE_INSTALL_LIBDIR@
-includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+libdir=@PKG_CONFIG_LIBDIR@
+includedir=@PKG_CONFIG_INCLUDEDIR@
 
 Name: shaderc
 Description: Tools and libraries for Vulkan shader compilation

cmake/shaderc_combined.pc.in

@@ -1,7 +1,7 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
-libdir=${prefix}/@CMAKE_INSTALL_LIBDIR@
-includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+libdir=@PKG_CONFIG_LIBDIR@
+includedir=@PKG_CONFIG_INCLUDEDIR@
 
 Name: shaderc
 Description: Tools and libraries for Vulkan shader compilation

cmake/shaderc_static.pc.in

@@ -1,7 +1,7 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
-libdir=${prefix}/@CMAKE_INSTALL_LIBDIR@
-includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+libdir=@PKG_CONFIG_LIBDIR@
+includedir=@PKG_CONFIG_INCLUDEDIR@
 
 Name: shaderc
 Description: Tools and libraries for Vulkan shader compilation

cmake/write_pkg_config.cmake

@@ -28,4 +28,6 @@ REGEX
 # CMake support "-dev" in the version.
 # If it's not a "-dev" version then ensure it ends with ".1"
 string(REGEX REPLACE "-dev.1" ".0" CURRENT_VERSION "${CURRENT_VERSION}.1")
+cmake_path(APPEND PKG_CONFIG_LIBDIR "\${exec_prefix}" "${CMAKE_INSTALL_LIBDIR}")
+cmake_path(APPEND PKG_CONFIG_INCLUDEDIR "\${prefix}" "${CMAKE_INSTALL_INCLUDEDIR}")
 configure_file(${TEMPLATE_FILE} ${OUT_FILE} @ONLY)