[libc++abi] Add LIBCXXABI_ENABLE_PIC cmake option

This is on by default, since on many platforms and configurations
libc++abi.a gets statically linked into shared libraries and/or
PIE executables.

This change is a followup to https://reviews.llvm.org/D60005 which
allows us to default to PIC code, but disable this if needed (for
example on WebAssembly where PIC code its currently compatible with
static linking).

Differential Revision: https://reviews.llvm.org/D60049

llvm-svn: 357551

libcxxabi/CMakeLists.txt

@@ -46,6 +46,7 @@ include(HandleCompilerRT)
 option(LIBCXXABI_ENABLE_EXCEPTIONS "Use exceptions." ON)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
+option(LIBCXXABI_ENABLE_PIC "Build Position-Independent Code, even in static library" ON)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
 option(LIBCXXABI_ENABLE_STATIC_UNWINDER "Statically link the LLVM unwinder." OFF)

libcxxabi/src/CMakeLists.txt

@@ -155,6 +155,10 @@ macro(cxxabi_object_library name)
                           COMPILE_FLAGS
                             "${LIBCXXABI_COMPILE_FLAGS}")
 
+  if(LIBCXXABI_ENABLE_PIC)
+    set_target_properties(${name} PROPERTIES POSITION_INDEPENDENT_CODE ON)
+  endif()
+
   if(ARGS_DEFINES)
     target_compile_definitions(${name} PRIVATE ${ARGS_DEFINES})
   endif()
@@ -177,7 +181,6 @@ else()
 endif()
 
 cxxabi_object_library(cxxabi_shared_objects)
-set_target_properties(cxxabi_shared_objects PROPERTIES POSITION_INDEPENDENT_CODE ON)
 
 set(cxxabi_static_sources $<TARGET_OBJECTS:cxxabi_static_objects>)
 set(cxxabi_shared_sources $<TARGET_OBJECTS:cxxabi_shared_objects>)