cmake: Treat xmpsdk headers as system ones

This is done so that when we use EXIV2_TEAM_EXTRA_WARNINGS we do not get
warnings about XMPSDK (we do not want to deal with those)

cmake/compilerFlags.cmake

@@ -61,6 +61,7 @@ if ( MINGW OR UNIX OR MSYS ) # MINGW, Linux, APPLE, CYGWIN
         endif()
 
         add_compile_options(-Wall -Wcast-align -Wpointer-arith -Wformat-security -Wmissing-format-attribute -Woverloaded-virtual -W)
+        add_compile_options(-Wno-error=format-nonliteral)
 
         # This seems to be causing issues in the Fedora_MinGW GitLab job
         #add_compile_options(-fasynchronous-unwind-tables)

src/CMakeLists.txt

@@ -133,7 +133,7 @@ set_target_properties( exiv2lib_int PROPERTIES
 )
 
 target_include_directories(exiv2lib_int PRIVATE ${ZLIB_INCLUDE_DIR})
-target_include_directories(exiv2lib PRIVATE 
+target_include_directories(exiv2lib SYSTEM PRIVATE 
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/xmpsdk/include>
     ${ZLIB_INCLUDE_DIR}
 )

unitTests/CMakeLists.txt

@@ -48,7 +48,7 @@ if (exiv2lib_COMPILE_DEFINITIONS)
     target_compile_definitions(unit_tests PRIVATE ${exiv2lib_COMPILE_DEFINITIONS})
 endif ()
 
-target_include_directories(unit_tests
+target_include_directories(unit_tests SYSTEM
     PRIVATE
         ${exiv2lib_INCLUDE_DIRECTORIES}
 )

xmpsdk/CMakeLists.txt

@@ -31,9 +31,9 @@ target_link_libraries(exiv2-xmp
         $<BUILD_INTERFACE:${EXPAT_LIBRARY}>
 )
 
-target_include_directories(exiv2-xmp
+target_include_directories(exiv2-xmp SYSTEM
     PRIVATE 
-        $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/xmpsdk/include>
+        ${PROJECT_SOURCE_DIR}/xmpsdk/include
         ${EXPAT_INCLUDE_DIR}
 )