[libunwind][CMake] Provide option to disable instalation of the library

[phosek]

Summary

This is useful in cases where we only build static library and
libunwind.a is combined with libc++abi.a into a single archive in which
case we don't want to have libunwind.a installed separately. The same
option is already provided by libcxx CMake build.

This change also adds the install-unwind target for consistency with the
libcxxabi and libcxx CMake build.

[beanz]

LGTM.

libunwind/trunk/CMakeLists.txt

 option(LIBUNWIND_ENABLE_CROSS_UNWINDING "Enable cross-platform unwinding support." OFF)
 option(LIBUNWIND_ENABLE_ARM_WMMX "Enable unwinding support for ARM WMMX registers." OFF)
 option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 option(LIBUNWIND_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 option(LIBUNWIND_INCLUDE_DOCS "Build the libunwind documentation." ${LLVM_INCLUDE_DOCS})
 
 set(LIBUNWIND_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
+option(LIBUNWIND_INSTALL_LIBRARY "Install the libunwind library." ON)
 set(LIBUNWIND_TARGET_TRIPLE "" CACHE STRING "Target triple for cross compiling.")
 set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
 set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
 
 if (NOT LIBUNWIND_ENABLE_SHARED AND NOT LIBUNWIND_ENABLE_STATIC)
   message(FATAL_ERROR "libunwind must be built as either a shared or static library.")
 endif()
 

libunwind/trunk/src/CMakeLists.txt

set_target_properties(unwind_static
                           LINK_FLAGS    "${LIBUNWIND_LINK_FLAGS}"
                           OUTPUT_NAME   "unwind")
   list(APPEND LIBUNWIND_TARGETS "unwind_static")
 endif()
 
 # Add a meta-target for both libraries.
 add_custom_target(unwind DEPENDS ${LIBUNWIND_TARGETS})
 
+if (LIBUNWIND_INSTALL_LIBRARY)
   install(TARGETS ${LIBUNWIND_TARGETS}
-  LIBRARY DESTINATION ${LIBUNWIND_INSTALL_PREFIX}lib${LIBUNWIND_LIBDIR_SUFFIX}
-  ARCHIVE DESTINATION ${LIBUNWIND_INSTALL_PREFIX}lib${LIBUNWIND_LIBDIR_SUFFIX})
+    LIBRARY DESTINATION ${LIBUNWIND_INSTALL_PREFIX}lib${LIBUNWIND_LIBDIR_SUFFIX} COMPONENT unwind
+    ARCHIVE DESTINATION ${LIBUNWIND_INSTALL_PREFIX}lib${LIBUNWIND_LIBDIR_SUFFIX} COMPONENT unwind)
+endif()
 
+if (NOT CMAKE_CONFIGURATION_TYPES AND LIBUNWIND_INSTALL_LIBRARY)
+  add_custom_target(install-unwind
+    DEPENDS unwind
+    COMMAND "${CMAKE_COMMAND}"
+            -DCMAKE_INSTALL_COMPONENT=unwind
+            -P "${LIBCXXABI_BINARY_DIR}/cmake_install.cmake")
+endif()