LibC: Symlink headers into the sysroot at configure-time

This removes the need to have the install_libc_headers target, since
LibC's headers will now get installed before anything gets built. By
extension, this also prevents said target from re-running on every
build.

Kernel/CMakeLists.txt

@@ -803,11 +803,10 @@ add_compile_definitions(KERNEL)
 add_link_options(LINKER:-z,notext)
 
 add_library(kernel_heap STATIC ${KERNEL_HEAP_SOURCES})
-add_dependencies(kernel_heap install_libc_headers)
 target_link_libraries(kernel_heap PUBLIC GenericClangPlugin)
 
 add_executable(Kernel ${SOURCES})
-add_dependencies(Kernel generate_EscapeSequenceStateMachine.h generate_version_header install_libc_headers)
+add_dependencies(Kernel generate_EscapeSequenceStateMachine.h generate_version_header)
 target_link_libraries(Kernel PUBLIC GenericClangPlugin)
 
 if("${SERENITY_ARCH}" STREQUAL "aarch64")

Kernel/Prekernel/CMakeLists.txt

@@ -40,7 +40,6 @@ add_compile_definitions(PREKERNEL)
 
 add_executable(${PREKERNEL_TARGET} ${SOURCES} $<TARGET_OBJECTS:KernelObject>)
 add_dependencies(${PREKERNEL_TARGET} Kernel)
-add_dependencies(${PREKERNEL_TARGET} install_libc_headers)
 target_compile_options(${PREKERNEL_TARGET} PRIVATE -no-pie -fno-pic -fno-threadsafe-statics)
 
 target_link_options(${PREKERNEL_TARGET} PRIVATE LINKER:-T ${CMAKE_CURRENT_SOURCE_DIR}/linker.ld -nostdlib LINKER:--no-pie)

Userland/DynamicLoader/CMakeLists.txt

@@ -8,7 +8,6 @@ target_compile_definitions(DynamicLoader_CompileOptions INTERFACE NO_TLS _DYNAMI
 target_compile_options(DynamicLoader_CompileOptions INTERFACE -fno-rtti -fpie -ffunction-sections -fdata-sections)
 target_link_options(DynamicLoader_CompileOptions INTERFACE -nolibc -nostdlib++ -nostartfiles -static-libgcc -fpie -Wl,--gc-sections)
 target_link_options(DynamicLoader_CompileOptions INTERFACE -fno-sanitize=undefined) # Sanitizer runtime is linked in manually
-add_dependencies(DynamicLoader_CompileOptions install_libc_headers)
 
 add_executable(Loader.so ${SOURCES})
 

Userland/Libraries/LibC/CMakeLists.txt

@@ -218,27 +218,20 @@ set(HEADERS
 )
 
 # ===== LibC headers =====
-add_custom_target(install_libc_headers)
-
-# Copy LibC's headers into the sysroot to satisfy libc++'s include priority requirements.
+# NOTE: We have to symlink LibC's headers into the sysroot to satisfy libc++'s include priority
+#       requirements.
 foreach(RELATIVE_HEADER_PATH IN LISTS HEADERS)
     get_filename_component(directory ${RELATIVE_HEADER_PATH} DIRECTORY)
+    get_filename_component(name ${RELATIVE_HEADER_PATH} NAME)
     string(REPLACE "../" "" subdirectory "${directory}")
     file(MAKE_DIRECTORY "${CMAKE_STAGING_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR}/${subdirectory}")
-    add_custom_command(
-        TARGET install_libc_headers
-        PRE_BUILD
-        COMMAND "${CMAKE_COMMAND}" -E copy_if_different "${RELATIVE_HEADER_PATH}" "${CMAKE_STAGING_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR}/${subdirectory}"
-        WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
-        VERBATIM
-    )
+    file(CREATE_LINK "${CMAKE_CURRENT_SOURCE_DIR}/${RELATIVE_HEADER_PATH}" "${CMAKE_STAGING_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR}/${subdirectory}/${name}" SYMBOLIC)
 endforeach()
 
 # ===== Start files =====
 # NOTE: We link all these against NoCoverage so that we don't break ports by requiring coverage
 #       symbols in runtime/startup objects.
 add_library(crt0 STATIC crt0.cpp)
-add_dependencies(crt0 install_libc_headers)
 target_link_libraries(crt0 PRIVATE NoCoverage)
 add_custom_command(
     TARGET crt0
@@ -249,7 +242,6 @@ add_custom_command(
 #        some convincing that this is the case.
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     add_library(crt0_shared STATIC crt0_shared.cpp)
-    add_dependencies(crt0_shared install_libc_headers)
     target_link_libraries(crt0_shared PRIVATE NoCoverage)
     add_custom_command(
         TARGET crt0_shared
@@ -283,7 +275,7 @@ else()
 endif()
 
 serenity_libc(LibC c)
-add_dependencies(LibC crt0 install_libc_headers)
+add_dependencies(LibC crt0)
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     add_dependencies(LibC crti crt0_shared crtn)
 endif()

Userland/Libraries/LibCrypt/CMakeLists.txt

@@ -3,7 +3,6 @@
 # To avoid a circular dependency chain with LibCrypt --> LibCrypto --> LibCore --> LibCrypt
 # We include the SHA2 implementation from LibCrypto here manually
 add_library(LibCryptSHA2 OBJECT ../LibCrypto/Hash/SHA2.cpp)
-add_dependencies(LibCryptSHA2 install_libc_headers)
 set_target_properties(LibCryptSHA2 PROPERTIES CXX_VISIBILITY_PRESET hidden)
 set_target_properties(LibCryptSHA2 PROPERTIES VISIBILITY_INLINES_HIDDEN ON)
 

Userland/Libraries/LibSanitizer/CMakeLists.txt

@@ -4,7 +4,6 @@ set(SOURCES
 )
 
 serenity_libc(LibUBSanitizer ubsan)
-add_dependencies(LibUBSanitizer install_libc_headers)
 target_link_options(LibUBSanitizer PRIVATE -nostdlib)
 
 add_library(DynamicLoader_LibUBSanitizer STATIC UBSanitizer.cpp)

Userland/Libraries/LibSystem/CMakeLists.txt

@@ -3,7 +3,6 @@ set(SOURCES
 )
 
 serenity_libc(LibSystem system)
-add_dependencies(LibSystem install_libc_headers)
 target_link_options(LibSystem PRIVATE -nostdlib)
 
 add_library(DynamicLoader_LibSystem STATIC ${SOURCES})

Userland/Libraries/LibTest/CMakeLists.txt

@@ -11,8 +11,3 @@ target_link_libraries(LibTest PRIVATE LibCore)
 
 add_library(LibTestMain OBJECT TestMain.cpp)
 add_library(JavaScriptTestRunnerMain OBJECT JavaScriptTestRunnerMain.cpp)
-
-if (SERENITYOS)
-    add_dependencies(LibTestMain install_libc_headers)
-    add_dependencies(JavaScriptTestRunnerMain install_libc_headers)
-endif()

Userland/Libraries/LibTimeZone/CMakeLists.txt

@@ -13,6 +13,3 @@ target_compile_definitions(LibTimeZone PRIVATE ENABLE_TIME_ZONE_DATA=$<BOOL:${EN
 # NOTE: These objects are used by the DynamicLoader, which is always built without coverage instrumentation.
 #       We could allow them to be instrumented for coverage if DynamicLoader built its own copy
 target_link_libraries(LibTimeZone PRIVATE NoCoverage)
-if (SERENITYOS)
-    add_dependencies(LibTimeZone install_libc_headers)
-endif()