Support ASan library on macOS for all generators.

This change allows macOS developers to use
`WITH_COMPILER_ASAN` with every generator.

`CMAKE_C_IMPLICIT_LINK_DIRECTORIES` on macOS points to
`Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/lib`
which is not where the Sanitizer libraries are.

To link the library, rpath could be used but that seems complex,
so linker flags are passed as the documentation says. [1]

If users have `ASAN_OPTIONS=detect_leaks=1` in their environment
variables, it should be removed to avoid a feature-unsupported error
while compiling.

[1]: http://clang.llvm.org/docs/AddressSanitizer.html#usage

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D8817

CMakeLists.txt

@@ -510,9 +510,21 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
 -fno-sanitize=alignment \
 ")
 
-    if(NOT MSVC) # not all sanitizers are supported with clang-cl, these two however are very vocal about it
+    if(MSVC)
+      # clang-cl doesn't support all sanitizers, but leak and object-size give errors/warnings.
+      set(_asan_defaults "${_asan_defaults}")
+    elseif(APPLE)
+      # AppleClang doesn't support all sanitizers, but leak gives error.
+      if(CMAKE_BUILD_TYPE MATCHES "Debug")
+        # Silence the warning that object-size is not effective in -O0.
+        set(_asan_defaults "${_asan_defaults}")
+      else()
+        set(_asan_defaults "${_asan_defaults} -fsanitize=object-size")
+      endif()
+    else()
       set(_asan_defaults "${_asan_defaults} -fsanitize=leak -fsanitize=object-size")
     endif()
+
     set(COMPILER_ASAN_CFLAGS "${_asan_defaults}" CACHE STRING "C flags for address sanitizer")
     mark_as_advanced(COMPILER_ASAN_CFLAGS)
     set(COMPILER_ASAN_CXXFLAGS "${_asan_defaults}" CACHE STRING "C++ flags for address sanitizer")
@@ -520,16 +532,31 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
 
     unset(_asan_defaults)
 
-    if(NOT MSVC)
-      find_library(COMPILER_ASAN_LIBRARY asan ${CMAKE_C_IMPLICIT_LINK_DIRECTORIES})
-    else()
+    if(MSVC)
         find_library(
           COMPILER_ASAN_LIBRARY NAMES clang_rt.asan-x86_64
         PATHS
         [HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\LLVM\\LLVM;]/lib/clang/7.0.0/lib/windows
         [HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\LLVM\\LLVM;]/lib/clang/6.0.0/lib/windows
       )
+    elseif(APPLE)
+      execute_process(COMMAND ${CMAKE_CXX_COMPILER} 
+        -print-file-name=lib 
+        OUTPUT_VARIABLE CLANG_LIB_DIR
+      )
+      string(STRIP "${CLANG_LIB_DIR}" CLANG_LIB_DIR)
+      find_library(
+        COMPILER_ASAN_LIBRARY NAMES libclang_rt.asan_osx_dynamic.dylib
+        PATHS 
+        "${CLANG_LIB_DIR}/darwin/"
+      )
+      unset(CLANG_LIB_DIR)
+    else()
+      find_library(
+        COMPILER_ASAN_LIBRARY asan ${CMAKE_C_IMPLICIT_LINK_DIRECTORIES}
+      )
     endif()
+
     mark_as_advanced(COMPILER_ASAN_LIBRARY)
   endif()
 endif()
@@ -823,6 +850,9 @@ if(NOT CMAKE_BUILD_TYPE MATCHES "Release")
     if(MSVC)
       set(COMPILER_ASAN_LINKER_FLAGS "/FUNCTIONPADMIN:6")
     endif()
+    if(APPLE)
+      set(COMPILER_ASAN_LINKER_FLAGS "-fno-omit-frame-pointer -fsanitize=address")
+    endif(APPLE)
     if(COMPILER_ASAN_LIBRARY)
       set(PLATFORM_LINKLIBS "${PLATFORM_LINKLIBS};${COMPILER_ASAN_LIBRARY}")
       set(PLATFORM_LINKFLAGS "${COMPILER_ASAN_LIBRARY} ${COMPILER_ASAN_LINKER_FLAGS}")