[CMake] Support passing FUCHSIA_SDK as the only variable

[phosek]

Summary

Now that the structure of Fuchsia SDK has been formalized, we no
longer need to pass all the different CFLAGS/LDFLAGS to the CMake
build separately, we can simply set the FUCHSIA_SDK variable and
derive all the necessary variables from that one inside the cache
file.

[mcgrathr]

lgtm

clang/cmake/caches/Fuchsia-stage2.cmake

 set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
 set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 -gline-tables-only -DNDEBUG" CACHE STRING "")
 
 set(FUCHSIA_BUILTINS_BUILD_TYPE Release CACHE STRING "")
 set(FUCHSIA_RUNTIMES_BUILD_TYPE Release CACHE STRING "")
 set(FUCHSIA_RUNTIMES_ENABLE_ASSERTIONS ON CACHE BOOL "")
 
+set(FUCHSIA_aarch64_NAME arm64)
+set(FUCHSIA_x86_64_NAME x64)
+foreach(target x86_64;aarch64)
+  set(FUCHSIA_${target}_COMPILER_FLAGS "-I${FUCHSIA_SDK}/pkg/fdio/include")
+  set(FUCHSIA_${target}_LINKER_FLAGS "-L${FUCHSIA_SDK}/arch/${FUCHSIA_${target}_NAME}/lib")
+  set(FUCHSIA_${target}_SYSROOT "${FUCHSIA_SDK}/arch/${FUCHSIA_${target}_NAME}/sysroot")
+endforeach()
+
 set(LLVM_BUILTIN_TARGETS "default;x86_64-fuchsia;aarch64-fuchsia" CACHE STRING "")
 
 # Set the per-target builtins options.
 foreach(target x86_64;aarch64)
   set(BUILTINS_${target}-fuchsia_CMAKE_SYSTEM_NAME Fuchsia CACHE STRING "")
   set(BUILTINS_${target}-fuchsia_CMAKE_BUILD_TYPE ${FUCHSIA_BUILTINS_BUILD_TYPE} CACHE STRING "")
-  set(BUILTINS_${target}-fuchsia_CMAKE_ASM_FLAGS ${FUCHSIA_${target}_C_FLAGS} CACHE PATH "")
-  set(BUILTINS_${target}-fuchsia_CMAKE_C_FLAGS ${FUCHSIA_${target}_C_FLAGS} CACHE PATH "")
-  set(BUILTINS_${target}-fuchsia_CMAKE_CXX_FLAGS ${FUCHSIA_${target}_CXX_FLAGS} CACHE PATH "")
-  set(BUILTINS_${target}-fuchsia_CMAKE_EXE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
+  set(BUILTINS_${target}-fuchsia_CMAKE_ASM_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
+  set(BUILTINS_${target}-fuchsia_CMAKE_C_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
+  set(BUILTINS_${target}-fuchsia_CMAKE_CXX_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
   set(BUILTINS_${target}-fuchsia_CMAKE_SHARED_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
   set(BUILTINS_${target}-fuchsia_CMAKE_MODULE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
+  set(BUILTINS_${target}-fuchsia_CMAKE_EXE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
   set(BUILTINS_${target}-fuchsia_CMAKE_SYSROOT ${FUCHSIA_${target}_SYSROOT} CACHE PATH "")
 endforeach()
 
 set(LLVM_RUNTIME_TARGETS "default;x86_64-fuchsia;aarch64-fuchsia;x86_64-fuchsia-asan:x86_64-fuchsia;aarch64-fuchsia-asan:aarch64-fuchsia" CACHE STRING "")
 
 # Set the default target runtimes options.
 if(NOT APPLE)
   set(LIBUNWIND_ENABLE_SHARED OFF CACHE BOOL "")
if(NOT APPLE)
   set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
 endif()
 
 # Set the per-target runtimes options.
 foreach(target x86_64;aarch64)
   set(RUNTIMES_${target}-fuchsia_CMAKE_SYSTEM_NAME Fuchsia CACHE STRING "")
   set(RUNTIMES_${target}-fuchsia_CMAKE_BUILD_TYPE ${FUCHSIA_RUNTIMES_BUILD_TYPE} CACHE STRING "")
   set(RUNTIMES_${target}-fuchsia_CMAKE_BUILD_WITH_INSTALL_RPATH ON CACHE STRING "")
-  set(RUNTIMES_${target}-fuchsia_CMAKE_ASM_FLAGS ${FUCHSIA_${target}_C_FLAGS} CACHE PATH "")
-  set(RUNTIMES_${target}-fuchsia_CMAKE_C_FLAGS ${FUCHSIA_${target}_C_FLAGS} CACHE PATH "")
-  set(RUNTIMES_${target}-fuchsia_CMAKE_CXX_FLAGS ${FUCHSIA_${target}_CXX_FLAGS} CACHE PATH "")
-  set(RUNTIMES_${target}-fuchsia_CMAKE_EXE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
+  set(RUNTIMES_${target}-fuchsia_CMAKE_ASM_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
+  set(RUNTIMES_${target}-fuchsia_CMAKE_C_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
+  set(RUNTIMES_${target}-fuchsia_CMAKE_CXX_FLAGS ${FUCHSIA_${target}_COMPILER_FLAGS} CACHE PATH "")
   set(RUNTIMES_${target}-fuchsia_CMAKE_SHARED_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
   set(RUNTIMES_${target}-fuchsia_CMAKE_MODULE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
+  set(RUNTIMES_${target}-fuchsia_CMAKE_EXE_LINKER_FLAGS ${FUCHSIA_${target}_LINKER_FLAGS} CACHE PATH "")
   set(RUNTIMES_${target}-fuchsia_CMAKE_SYSROOT ${FUCHSIA_${target}_SYSROOT} CACHE PATH "")
   set(RUNTIMES_${target}-fuchsia_LLVM_ENABLE_ASSERTIONS ${FUCHSIA_RUNTIMES_ENABLE_ASSERTIONS} CACHE BOOL "")
   set(RUNTIMES_${target}-fuchsia_LIBUNWIND_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_${target}-fuchsia_LIBCXXABI_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_${target}-fuchsia_LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
   set(RUNTIMES_${target}-fuchsia_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
   set(RUNTIMES_${target}-fuchsia_SANITIZER_USE_COMPILER_RT ON CACHE BOOL "")