This patch makes pugixml install its headers to a standard location when
built as a shared library.

Taken from this upstream commit:
https://github.com/zeux/pugixml/commit/daeb8013b20f9c47e85730faaa4131064a1f9c2e

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 90fa6793..d7bc1b20 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@ project(pugixml)
 
 option(BUILD_SHARED_LIBS "Build shared instead of static library" OFF)
 option(BUILD_TESTS "Build tests" OFF)
-option(BUILD_PKGCONFIG "Build in PKGCONFIG mode" OFF)
+option(USE_VERSIONED_LIBDIR "Use a private subdirectory to install the headers and libs" OFF)
 
 set(BUILD_DEFINES "" CACHE STRING "Build defines")
 
@@ -55,7 +55,7 @@ endif()
 set_target_properties(pugixml PROPERTIES VERSION 1.9 SOVERSION 1)
 get_target_property(PUGIXML_VERSION_STRING pugixml VERSION)
 
-if(BUILD_PKGCONFIG)
+if(USE_VERSIONED_LIBDIR)
 	# Install library into its own directory under LIBDIR
 	set(INSTALL_SUFFIX /pugixml-${PUGIXML_VERSION_STRING})
 endif()
@@ -71,10 +71,8 @@ install(TARGETS pugixml EXPORT pugixml-config
 install(FILES ${HEADERS} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}${INSTALL_SUFFIX})
 install(EXPORT pugixml-config DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/pugixml)
 
-if(BUILD_PKGCONFIG)
-	configure_file(scripts/pugixml.pc.in ${PROJECT_BINARY_DIR}/pugixml.pc @ONLY)
-	install(FILES ${PROJECT_BINARY_DIR}/pugixml.pc DESTINATION ${CMAKE_INSTALL_PREFIX}/lib/pkgconfig)
-endif()
+configure_file(scripts/pugixml.pc.in ${PROJECT_BINARY_DIR}/pugixml.pc @ONLY)
+install(FILES ${PROJECT_BINARY_DIR}/pugixml.pc DESTINATION ${CMAKE_INSTALL_PREFIX}/lib/pkgconfig)
 
 if(BUILD_TESTS)
 	file(GLOB TEST_SOURCES tests/*.cpp)
diff --git a/scripts/pugixml.pc.in b/scripts/pugixml.pc.in
index 3c97c28d..804c4d38 100644
--- a/scripts/pugixml.pc.in
+++ b/scripts/pugixml.pc.in
@@ -1,11 +1,11 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
-includedir=${prefix}/include/pugixml-@PUGIXML_VERSION_STRING@
-libdir=${exec_prefix}/lib/pugixml-@PUGIXML_VERSION_STRING@
+includedir=${prefix}/include@INSTALL_SUFFIX@
+libdir=${exec_prefix}/lib@INSTALL_SUFFIX@
 
 Name: pugixml
 Description: Light-weight, simple and fast XML parser for C++ with XPath support.
 URL: http://pugixml.org/
 Version: @PUGIXML_VERSION_STRING@
 Cflags: -I${includedir}
-Libs: -L${libdir} -lpugixml
\ No newline at end of file
+Libs: -L${libdir} -lpugixml
