CMake: don't put linker flags in compile-flags variables

CMakeLists.txt

@@ -192,7 +192,7 @@ include( CMakeColors )
 #
 set( CMAKE_CXX_STANDARD 17 )
 set( CMAKE_CXX_STANDARD_REQUIRED ON )
-set( CMAKE_CXX_FLAGS                "${CMAKE_CXX_FLAGS} -Wall -Werror=return-type -Wl,--no-undefined" )
+set( CMAKE_CXX_FLAGS                "${CMAKE_CXX_FLAGS} -Wall -Werror=return-type" )
 set( CMAKE_CXX_FLAGS_DEBUG          "-g ${CMAKE_CXX_FLAGS_DEBUG}" )
 set( CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG" )
 set( CMAKE_CXX_FLAGS_RELEASE        "-O3 -DNDEBUG" )
@@ -206,7 +206,7 @@ set( CMAKE_C_FLAGS_MINSIZEREL       "-Os -DNDEBUG" )
 set( CMAKE_C_FLAGS_RELEASE          "-O4 -DNDEBUG" )
 set( CMAKE_C_FLAGS_RELWITHDEBINFO   "-O2 -g" )
 
-set( CMAKE_SHARED_LINKER_FLAGS "-Wl,--no-undefined" )
+set( CMAKE_SHARED_LINKER_FLAGS      "-Wl,--no-undefined -Wl,--fatal-warnings" )
 
 if( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
     message( STATUS "Found Clang ${CMAKE_CXX_COMPILER_VERSION}, setting up Clang-specific compiler flags." )
@@ -243,7 +243,7 @@ if( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
     set( CALAMARES_AUTOMOC_OPTIONS "-butils/moc-warnings.h" )
     set( CALAMARES_AUTOUIC_OPTIONS --include utils/moc-warnings.h )
 else()
-    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wl,--fatal-warnings -Wnon-virtual-dtor -Woverloaded-virtual" )
+    set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wnon-virtual-dtor -Woverloaded-virtual" )
 
     set( SUPPRESS_3RDPARTY_WARNINGS "" )