Fix bug where `config.asan_dynamic` in generated ASan `lit.site.cfg` files was set to `False` for macOS. It should actually be `True` because dylibs are the only supported form of the ASan runtime on Apple platforms.

test/asan/CMakeLists.txt

else()
     set(ASAN_TEST_TARGET_ARCH ${arch})
   endif()
 
   set(ASAN_TEST_APPLE_PLATFORM "osx")
 
   string(TOLOWER "-${arch}-${OS_NAME}" ASAN_TEST_CONFIG_SUFFIX)
   get_bits_for_arch(${arch} ASAN_TEST_BITS)
   get_test_cc_for_arch(${arch} ASAN_TEST_TARGET_CC ASAN_TEST_TARGET_CFLAGS)
-  if(ANDROID)
+  if(ANDROID OR APPLE)
     set(ASAN_TEST_DYNAMIC True)
   else()
     set(ASAN_TEST_DYNAMIC False)
   endif()
   string(TOUPPER ${arch} ARCH_UPPER_CASE)
   set(CONFIG_NAME ${ARCH_UPPER_CASE}${OS_NAME}Config)
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in