Reland "[CMake] Support statically linking dependencies only to shared or static library"

This is a reland of commit r337668.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@337814 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index caadb79..adfe8c6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,6 +84,13 @@
 option(LIBCXXABI_ENABLE_SHARED "Build libc++abi as a shared library." ON)
 option(LIBCXXABI_ENABLE_STATIC "Build libc++abi as a static library." ON)
 
+cmake_dependent_option(LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY
+  "Statically link the LLVM unwinder to static library" ON
+  "LIBCXXABI_ENABLE_STATIC_UNWINDER;LIBCXXABI_ENABLE_STATIC" OFF)
+cmake_dependent_option(LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY
+  "Statically link the LLVM unwinder to shared library" ON
+  "LIBCXXABI_ENABLE_STATIC_UNWINDER;LIBCXXABI_ENABLE_SHARED" OFF)
+
 option(LIBCXXABI_BAREMETAL "Build libc++abi for baremetal targets." OFF)
 # The default terminate handler attempts to demangle uncaught exceptions, which
 # causes extra I/O and demangling code to be pulled in.
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5a929cf..9827879 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -61,12 +61,19 @@
   # Prefer using the in-tree version of libunwind, either shared or static. If
   # none are found fall back to using -lunwind.
   # FIXME: Is it correct to prefer the static version of libunwind?
-  if (NOT LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
-    list(APPEND LIBCXXABI_LIBRARIES unwind_shared)
-  elseif (LIBCXXABI_ENABLE_STATIC_UNWINDER AND (TARGET unwind_static OR HAVE_LIBUNWIND))
-    list(APPEND LIBCXXABI_LIBRARIES unwind_static)
+  if (NOT LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
+    list(APPEND LIBCXXABI_SHARED_LIBRARIES unwind_shared)
+  elseif (LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY AND (TARGET unwind_static OR HAVE_LIBUNWIND))
+    list(APPEND LIBCXXABI_SHARED_LIBRARIES unwind_static)
   else()
-    list(APPEND LIBCXXABI_LIBRARIES unwind)
+    list(APPEND LIBCXXABI_SHARED_LIBRARIES unwind)
+  endif()
+  if (NOT LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
+    list(APPEND LIBCXXABI_STATIC_LIBRARIES unwind_shared)
+  elseif (LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY AND (TARGET unwind_static OR HAVE_LIBUNWIND))
+      # We handle this by directly merging libunwind objects into libc++abi.
+  else()
+    list(APPEND LIBCXXABI_STATIC_LIBRARIES unwind)
   endif()
 else()
   add_library_flags_if(LIBCXXABI_HAS_GCC_S_LIB gcc_s)
@@ -130,7 +137,7 @@
   if(COMMAND llvm_setup_rpath)
     llvm_setup_rpath(cxxabi_shared)
   endif()
-  target_link_libraries(cxxabi_shared ${LIBCXXABI_LIBRARIES})
+  target_link_libraries(cxxabi_shared ${LIBCXXABI_LIBRARIES} ${LIBCXXABI_SHARED_LIBRARIES})
   set_target_properties(cxxabi_shared
                         PROPERTIES
                           CXX_EXTENSIONS
@@ -155,13 +162,13 @@
 # Build the static library.
 if (LIBCXXABI_ENABLE_STATIC)
   set(cxxabi_static_sources $<TARGET_OBJECTS:cxxabi_objects>)
-  if (LIBCXXABI_USE_LLVM_UNWINDER AND LIBCXXABI_ENABLE_STATIC_UNWINDER)
+  if (LIBCXXABI_USE_LLVM_UNWINDER AND LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY)
     if (TARGET unwind_static OR HAVE_LIBUNWIND)
       list(APPEND cxxabi_static_sources $<TARGET_OBJECTS:unwind_objects>)
     endif()
   endif()
   add_library(cxxabi_static STATIC ${cxxabi_static_sources})
-  target_link_libraries(cxxabi_static ${LIBCXXABI_LIBRARIES})
+  target_link_libraries(cxxabi_static ${LIBCXXABI_LIBRARIES} ${LIBCXXABI_STATIC_LIBRARIES})
   set_target_properties(cxxabi_static
                         PROPERTIES
                           CXX_EXTENSIONS