Wrap CMAKE_SHARED_LIBRARY_CXX_FLAGS in quotes.

The variable is empty on some platforms (Windows), would cause issues.

src/Plugins/MagnumFont/CMakeLists.txt

@@ -31,7 +31,7 @@ set(MagnumFont_HEADERS
     MagnumFont.h)
 
 add_library(MagnumFontObjects OBJECT ${MagnumFont_SOURCES})
-set_target_properties(MagnumFontObjects PROPERTIES COMPILE_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
+set_target_properties(MagnumFontObjects PROPERTIES COMPILE_FLAGS "${CMAKE_SHARED_LIBRARY_CXX_FLAGS}")
 
 add_plugin(MagnumFont ${MAGNUM_PLUGINS_FONT_INSTALL_DIR}
     MagnumFont.conf

src/Plugins/MagnumFontConverter/CMakeLists.txt

@@ -31,7 +31,7 @@ set(MagnumFontConverter_HEADERS
     MagnumFontConverter.h)
 
 add_library(MagnumFontConverterObjects OBJECT ${MagnumFontConverter_SOURCES})
-set_target_properties(MagnumFontConverterObjects PROPERTIES COMPILE_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
+set_target_properties(MagnumFontConverterObjects PROPERTIES COMPILE_FLAGS "${CMAKE_SHARED_LIBRARY_CXX_FLAGS}")
 
 add_plugin(MagnumFontConverter ${MAGNUM_PLUGINS_FONTCONVERTER_INSTALL_DIR}
     MagnumFontConverter.conf

src/Plugins/TgaImageConverter/CMakeLists.txt

@@ -29,7 +29,7 @@ set(TgaImageConverter_HEADERS
     TgaImageConverter.h)
 
 add_library(TgaImageConverterObjects OBJECT ${TgaImageConverter_SRCS})
-set_target_properties(TgaImageConverterObjects PROPERTIES COMPILE_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
+set_target_properties(TgaImageConverterObjects PROPERTIES COMPILE_FLAGS "${CMAKE_SHARED_LIBRARY_CXX_FLAGS}")
 
 add_plugin(TgaImageConverter ${MAGNUM_PLUGINS_IMAGECONVERTER_INSTALL_DIR}
     TgaImageConverter.conf

src/Plugins/TgaImporter/CMakeLists.txt

@@ -30,7 +30,7 @@ set(TgaImporter_HEADERS
     TgaImporter.h)
 
 add_library(TgaImporterObjects OBJECT ${TgaImporter_SRCS})
-set_target_properties(TgaImporterObjects PROPERTIES COMPILE_FLAGS ${CMAKE_SHARED_LIBRARY_CXX_FLAGS})
+set_target_properties(TgaImporterObjects PROPERTIES COMPILE_FLAGS "${CMAKE_SHARED_LIBRARY_CXX_FLAGS}")
 
 add_plugin(TgaImporter ${MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR}
     TgaImporter.conf