CMake: Make libc.a self-contained

Previously, libc.a contained undefined symbols from ssp and libsystem,
which caused static compilation to fail.

We now generate libc.a with a custom CMake rule that combines all
object files from libc, ssp and libsystem to form libc.a

Closes #5758.

Userland/Libraries/LibC/CMakeLists.txt

@@ -85,11 +85,31 @@ add_custom_command(
 
 set(SOURCES ${LIBC_SOURCES} ${AK_SOURCES} ${ELF_SOURCES} ${ASM_SOURCES})
 
-serenity_libc_static(LibCStatic c)
-target_link_libraries(LibCStatic crt0 ssp system)
-add_dependencies(LibCStatic LibM LibSystem)
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static-libstdc++")
+add_library(LibCStaticWithoutDeps STATIC ${SOURCES})
+target_link_libraries(LibCStaticWithoutDeps crt0 ssp)
+add_dependencies(LibCStaticWithoutDeps LibM LibSystem)
+
+add_custom_target(LibCStatic
+        COMMAND ${CMAKE_AR} -x $<TARGET_FILE:LibCStaticWithoutDeps>
+        COMMAND ${CMAKE_AR} -x $<TARGET_FILE:ssp>
+        COMMAND ${CMAKE_AR} -x $<TARGET_FILE:LibSystemStatic>
+        COMMAND ${CMAKE_AR} -qcs ${CMAKE_CURRENT_BINARY_DIR}/libc.a *.o
+        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+        DEPENDS LibCStaticWithoutDeps ssp LibSystemStatic
+        )
+
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/libc.a DESTINATION ${CMAKE_INSTALL_PREFIX}/usr/lib/)
+file(GLOB TEMP_OBJ_FILES ${CMAKE_CURRENT_BINARY_DIR}/*.o)
+set_property(
+        TARGET LibCStatic
+        APPEND
+        PROPERTY ADDITIONAL_CLEAN_FILES ${TEMP_OBJ_FILES}
+)
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static-libstdc++")
 serenity_libc(LibC c)
 target_link_libraries(LibC crt0 ssp system)
-add_dependencies(LibC LibM LibSystem)
+
+# We mark LibCStatic as a dependency of LibC because this triggers the build of the LibCStatic target
+add_dependencies(LibC LibM LibSystem LibCStatic)

Userland/Libraries/LibSystem/CMakeLists.txt

@@ -5,3 +5,6 @@ set(SOURCES
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -nostdlib")
 serenity_libc(LibSystem system)
 target_include_directories(LibSystem PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+add_library(LibSystemStatic STATIC ${SOURCES})
+target_include_directories(LibSystemStatic PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})