[CMake] Update CMake cache file for the ARM/Aarch64 cross toolchain builds. NFC.

* generate Clang configuration file with provided target sysroot (TOOLCHAIN_TARGET_SYSROOTFS)
* explicitly pass provided target sysroot into the compiler-rt tests configuration.
* added ability to configure a type of the build libraries -- shared or static
  (TOOLCHAIN_SHARED_LIBS, default OFF)

Author: vvereschaka

clang/cmake/caches/CrossWinToARMLinux.cmake

@@ -6,21 +6,23 @@
 # on Windows platform.
 #
 # NOTE: the build requires a development ARM Linux root filesystem to use
-# proper target platform depended library and header files:
-#  - create <full-path-to-clang-configs> directory and put the clang configuration
-#    file named <TOOLCHAIN_TARGET_TRIPLE>.cfg into it.
-#  - add the `--sysroot=<path-to-develop-arm-linux-root-fs>` argument into
-#    this configuration file.
-#  - add other necessary target depended clang arguments there, 
-#    such as '-mcpu=cortex-a78' & etc.
+# proper target platform depended library and header files.
+#
+# The build generates a proper clang configuration file with stored
+# --sysroot argument for specified target triple. Also it is possible
+# to specify configuration path via CMake arguments, such as
+#   -DCLANG_CONFIG_FILE_USER_DIR=<full-path-to-clang-configs>
+# and/or
+#   -DCLANG_CONFIG_FILE_SYSTEM_DIR=<full-path-to-clang-configs>
 #
 # See more details here: https://clang.llvm.org/docs/UsersManual.html#configuration-files
 #
 # Configure:
 #  cmake -G Ninja ^
 #       -DTOOLCHAIN_TARGET_TRIPLE=aarch64-unknown-linux-gnu ^
+#       -DTOOLCHAIN_TARGET_SYSROOTFS=<path-to-develop-arm-linux-root-fs> ^
+#       -DTOOLCHAIN_SHARED_LIBS=OFF ^ 
 #       -DCMAKE_INSTALL_PREFIX=../install ^
-#       -DCLANG_CONFIG_FILE_USER_DIR=<full-path-to-clang-configs> ^
 #       -DCMAKE_CXX_FLAGS="-D__OPTIMIZE__" ^
 #       -DREMOTE_TEST_HOST="<hostname>" ^
 #       -DREMOTE_TEST_USER="<ssh_user_name>" ^
@@ -81,6 +83,20 @@ endif()
 
 message(STATUS "Toolchain target triple: ${TOOLCHAIN_TARGET_TRIPLE}")
 
+if (DEFINED TOOLCHAIN_TARGET_SYSROOTFS)
+  message(STATUS "Toolchain target sysroot: ${TOOLCHAIN_TARGET_SYSROOTFS}")
+  # Store the --sysroot argument for the compiler-rt test flags.
+  set(sysroot_flags --sysroot='${TOOLCHAIN_TARGET_SYSROOTFS}')
+  # Generate the clang configuration file for the specified target triple
+  # and store --sysroot in this file.
+  file(WRITE "${CMAKE_BINARY_DIR}/bin/${TOOLCHAIN_TARGET_TRIPLE}.cfg" ${sysroot_flags})
+endif()
+
+# Build the shared libraries for libc++/libc++abi/libunwind.
+if (NOT DEFINED TOOLCHAIN_SHARED_LIBS)
+  set(TOOLCHAIN_SHARED_LIBS OFF)
+endif()
+ 
 if (NOT DEFINED LLVM_TARGETS_TO_BUILD)
   if ("${TOOLCHAIN_TARGET_TRIPLE}" MATCHES "^(armv|arm32)+")
     set(LLVM_TARGETS_TO_BUILD "ARM" CACHE STRING "")
@@ -183,20 +199,21 @@ set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_COMPILER_RT_CAN_EXECUTE_TESTS
 
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_COMPILER_RT_USE_BUILTINS_LIBRARY          ON CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_COMPILER_RT_CXX_LIBRARY                   libcxx CACHE STRING "")
-# Tell Clang to seach C++ headers alongside with the just-built binaries for the C++ compiler-rt tests.
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_COMPILER_RT_TEST_COMPILER_CFLAGS          "--stdlib=libc++" CACHE STRING "")
-
+# The compiler-rt tests disable the clang configuration files during the execution by setting CLANG_NO_DEFAULT_CONFIG=1
+# and drops out the --sysroot from there. Provide it explicity via the test flags here if target sysroot has been specified.
+set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_COMPILER_RT_TEST_COMPILER_CFLAGS          "--stdlib=libc++ ${sysroot_flags}" CACHE STRING "")
+  
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBUNWIND_USE_COMPILER_RT                 ON CACHE BOOL "")
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBUNWIND_ENABLE_SHARED                   OFF CACHE BOOL "")
+set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBUNWIND_ENABLE_SHARED                   ${TOOLCHAIN_SHARED_LIBS} CACHE BOOL "")
 
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_USE_LLVM_UNWINDER               ON CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_ENABLE_STATIC_UNWINDER          ON CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_USE_COMPILER_RT                 ON CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS   OFF CACHE BOOL "")
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_ENABLE_SHARED                   OFF CACHE BOOL "")
+set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXXABI_ENABLE_SHARED                   ${TOOLCHAIN_SHARED_LIBS} CACHE BOOL "")
 
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_USE_COMPILER_RT                    ON CACHE BOOL "")
-set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_SHARED                      OFF CACHE BOOL "")
+set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_SHARED                      ${TOOLCHAIN_SHARED_LIBS} CACHE BOOL "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ABI_VERSION                        ${LIBCXX_ABI_VERSION} CACHE STRING "")
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_CXX_ABI                            "libcxxabi" CACHE STRING "")    #!!!
 set(RUNTIMES_${TOOLCHAIN_TARGET_TRIPLE}_LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS      ON CACHE BOOL "")