Add -funwind-tables to CMAKE_C_FLAGS.

Without -funwind-tables, the compiler won't generate the unwinding
table for these C functions.  However, the functions in libunwind,
such as `_Unwind_Backtrace()`, WILL unwind stack to get the backtrace.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@226823 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index aaada04..6be1e15 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -164,6 +164,7 @@
   endif()
 endmacro()
 
+set(LIBCXXABI_C_FLAGS "")
 set(LIBCXXABI_CXX_FLAGS "")
 set(LIBCXXABI_COMPILE_FLAGS "")
 set(LIBCXXABI_LINK_FLAGS "")
@@ -216,6 +217,8 @@
 append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_FSTRICT_ALIASING_FLAG -fstrict-aliasing)
 append_if(LIBCXXABI_CXX_FLAGS LIBCXXABI_HAS_EHSC_FLAG -EHsc)
 
+append_if(LIBCXXABI_C_FLAGS LIBCXXABI_HAS_FUNWIND_TABLES -funwind-tables)
+
 # Assert
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 if (LIBCXXABI_ENABLE_ASSERTIONS)
@@ -260,6 +263,7 @@
           "--sysroot ${LIBCXXABI_SYSROOT}")
 string(REPLACE ";" " " LIBCXXABI_CXX_FLAGS "${LIBCXXABI_CXX_FLAGS}")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LIBCXXABI_CXX_FLAGS}")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${LIBCXXABI_C_FLAGS}")
 
 #===============================================================================
 # Setup Source Code