[CMake] Link to compiler-rt if LIBUNWIND_USE_COMPILER_RT is ON.

Summary:
If `-nodefaultlibs` is given, we weren't actually linking to it. This
was true irrespective of passing `-rtlib=compiler-rt` (see previous
patch). Now we explicitly link it to handle that case.

I wonder if we should be linking these libraries only if we're using
`-nodefaultlibs`...

Reviewers: beanz

Subscribers: dberris, mgorny, christof, chrib, cfe-commits

Differential Revision: https://reviews.llvm.org/D51657

llvm-svn: 343990

libunwind/cmake/config-ix.cmake

@@ -7,6 +7,7 @@ check_library_exists(c fopen "" LIBUNWIND_HAS_C_LIB)
 
 if (NOT LIBUNWIND_USE_COMPILER_RT)
   check_library_exists(gcc_s __gcc_personality_v0 "" LIBUNWIND_HAS_GCC_S_LIB)
+  check_library_exists(gcc __absvdi2 "" LIBUNWIND_HAS_GCC_LIB)
 endif()
 
 # libunwind is built with -nodefaultlibs, so we want all our checks to also
@@ -25,8 +26,13 @@ if (LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   if (LIBUNWIND_USE_COMPILER_RT)
     find_compiler_rt_library(builtins LIBUNWIND_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBUNWIND_BUILTINS_LIBRARY}")
-  elseif (LIBUNWIND_HAS_GCC_S_LIB)
-    list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
+  else ()
+    if (LIBUNWIND_HAS_GCC_S_LIB)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
+    endif ()
+    if (LIBUNWIND_HAS_GCC_LIB)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES gcc)
+    endif ()
   endif ()
   if (MINGW)
     # Mingw64 requires quite a few "C" runtime libraries in order for basic

libunwind/src/CMakeLists.txt

@@ -53,7 +53,12 @@ set(LIBUNWIND_SOURCES
 # Generate library list.
 set(libraries)
 append_if(libraries LIBUNWIND_HAS_C_LIB c)
-append_if(libraries LIBUNWIND_HAS_GCC_S_LIB gcc_s)
+if (LIBUNWIND_USE_COMPILER_RT)
+  list(APPEND libraries "${LIBUNWIND_BUILTINS_LIBRARY}")
+else()
+  append_if(libraries LIBUNWIND_HAS_GCC_S_LIB gcc_s)
+  append_if(libraries LIBUNWIND_HAS_GCC_LIB gcc)
+endif()
 append_if(libraries LIBUNWIND_HAS_DL_LIB dl)
 if (LIBUNWIND_ENABLE_THREADS)
   append_if(libraries LIBUNWIND_HAS_PTHREAD_LIB pthread)