Toolchain: Use Platform/SerenityOS.cmake in LLVM toolchain build

By setting CMAKE_MODULE_PATH in the LLVM initial cache scripts, we can
make the "SerenityOS" CMAKE_SYSTEM_NAME usable in the builds of
compiler-rt, libunwind, libcxxabi and libcxx.

This simplifies some toolchain patches and brings the cross-compiler
patches closer to the Port's patches, and closer to something
upstreamable.

Toolchain/BuildClang.sh

@@ -285,6 +285,7 @@ pushd "$DIR/Build/clang"
             -DSERENITY_x86_64-pc-serenity_SYSROOT="$BUILD/x86_64clang/Root" \
             -DSERENITY_aarch64-pc-serenity_SYSROOT="$BUILD/aarch64clang/Root" \
             -DCMAKE_INSTALL_PREFIX="$PREFIX" \
+            -DSERENITY_MODULE_PATH="$DIR/CMake" \
             -C "$DIR/CMake/LLVMConfig.cmake" \
             ${dev:+"-DLLVM_CCACHE_BUILD=ON"} \
             ${ci:+"-DLLVM_CCACHE_BUILD=ON"} \
@@ -318,6 +319,7 @@ pushd "$DIR/Build/clang"
                 -DSERENITY_TOOLCHAIN_ARCH="$arch" \
                 -DSERENITY_TOOLCHAIN_ROOT="$PREFIX" \
                 -DSERENITY_BUILD_DIR="$BUILD/${arch}clang/" \
+                -DSERENITY_MODULE_PATH="$DIR/CMake" \
                 -DCMAKE_INSTALL_PREFIX="$PREFIX" \
                 -C "$DIR/CMake/LLVMRuntimesConfig.cmake"
 

Toolchain/CMake/LLVMConfig.cmake

@@ -1,5 +1,9 @@
 # This file specifies the options used for building the Clang compiler, LLD linker and the compiler builtins library
 
+# Note: We force the cmake module path for all dependent projects to include our custom directory
+# That has the Platform/SerenityOS.cmake definition
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${SERENITY_MODULE_PATH}" CACHE STRING "Modules for CMake")
+
 set(CMAKE_BUILD_TYPE Release CACHE STRING "")
 
 set(LLVM_TARGETS_TO_BUILD "X86;AArch64" CACHE STRING "")
@@ -35,10 +39,14 @@ foreach(target i686-pc-serenity;x86_64-pc-serenity;aarch64-pc-serenity)
     set(RUNTIMES_${target}_COMPILER_RT_BUILD_PROFILE OFF CACHE BOOL "")
     set(RUNTIMES_${target}_COMPILER_RT_BUILD_XRAY OFF CACHE BOOL "")
     set(RUNTIMES_${target}_COMPILER_RT_BUILD_ORC OFF CACHE BOOL "")
+    set(RUNTIMES_${target}_CMAKE_SYSTEM_NAME SerenityOS CACHE STRING "")
+    set(RUNTIMES_${target}_CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} CACHE STRING "")
 
     set(BUILTINS_${target}_CMAKE_BUILD_TYPE Release CACHE STRING "")
     set(BUILTINS_${target}_CMAKE_SYSROOT ${SERENITY_${target}_SYSROOT} CACHE PATH "")
     set(BUILTINS_${target}_COMPILER_RT_EXCLUDE_ATOMIC_BUILTIN OFF CACHE BOOL "")
+    set(BUILTINS_${target}_CMAKE_SYSTEM_NAME SerenityOS CACHE STRING "")
+    set(BUILTINS_${target}_CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} CACHE STRING "")
 endforeach()
 
 set(LLVM_TOOLCHAIN_TOOLS

Toolchain/CMake/LLVMRuntimesConfig.cmake

@@ -1,9 +1,14 @@
 # This file specifies the options used for building the various LLVM runtime libraries
 
+# Note: We force the cmake module path for all dependent projects to include our custom directory
+# That has the Platform/SerenityOS.cmake definition
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${SERENITY_MODULE_PATH}" CACHE STRING "Modules for CMake")
+
 set(CMAKE_BUILD_TYPE Release CACHE STRING "")
 
 set(LLVM_ENABLE_RUNTIMES "libcxx;libcxxabi;libunwind" CACHE STRING "")
 
+set(CMAKE_SYSTEM_NAME SerenityOS CACHE STRING "")
 set(target_triple ${SERENITY_TOOLCHAIN_ARCH}-pc-serenity)
 
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ON CACHE BOOL "")

Toolchain/Patches/llvm.patch

@@ -592,6 +592,19 @@ index ba9f96384..4aecfeee2 100644
      return;
  
    case llvm::Triple::Win32:
+diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
+index 39b9120f0..1a49ac3e5 100644
+--- a/compiler-rt/cmake/config-ix.cmake
++++ b/compiler-rt/cmake/config-ix.cmake
+@@ -684,7 +684,7 @@ endif()
+ 
+ # TODO: Add builtins support.
+ 
+-if (CRT_SUPPORTED_ARCH AND OS_NAME MATCHES "Linux" AND NOT LLVM_USE_SANITIZER)
++if (CRT_SUPPORTED_ARCH AND OS_NAME MATCHES "Linux|SerenityOS" AND NOT LLVM_USE_SANITIZER)
+   set(COMPILER_RT_HAS_CRT TRUE)
+ else()
+   set(COMPILER_RT_HAS_CRT FALSE)
 diff --git a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake b/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
 index ad2820b32..deaa2c380 100644
 --- a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
@@ -736,26 +749,18 @@ index d5ab8fb3b..5039c1987 100644
      // Newlib has a 257-entry table in ctype_.c, where (char)0 starts at [1].
      return _ctype_ + 1;
 diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
-index 0c3419390..75f8b552b 100644
+index 0c3419390..7673b9183 100644
 --- a/llvm/cmake/modules/HandleLLVMOptions.cmake
 +++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
-@@ -228,11 +228,11 @@ endif()
+@@ -228,7 +228,7 @@ endif()
  
  # Pass -Wl,-z,defs. This makes sure all symbols are defined. Otherwise a DSO
  # build might work on ELF but fail on MachO/COFF.
 -if(NOT (CMAKE_SYSTEM_NAME MATCHES "Darwin|FreeBSD|OpenBSD|DragonFly|AIX|SunOS|OS390" OR
--        WIN32 OR CYGWIN) AND
++if(NOT (CMAKE_SYSTEM_NAME MATCHES "Darwin|FreeBSD|OpenBSD|DragonFly|AIX|SunOS|OS390|SerenityOS" OR
--   NOT LLVM_USE_SANITIZER)
+         WIN32 OR CYGWIN) AND
--  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,defs")
+    NOT LLVM_USE_SANITIZER)
--endif()
+   set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,defs")
-+#if(NOT (CMAKE_SYSTEM_NAME MATCHES "Darwin|FreeBSD|OpenBSD|DragonFly|AIX|SunOS|OS390" OR
-+#        WIN32 OR CYGWIN) AND
-+#   NOT LLVM_USE_SANITIZER)
-+#  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,defs")
-+#endif()
- 
- # Pass -Wl,-z,nodelete. This makes sure our shared libraries are not unloaded
- # by dlclose(). We need that since the CLI API relies on cross-references
 diff --git a/llvm/include/llvm/ADT/Triple.h b/llvm/include/llvm/ADT/Triple.h
 index 76f351405..b81556c55 100644
 --- a/llvm/include/llvm/ADT/Triple.h