build: suppress Xcode warnings (AcademySoftwareFoundation#3940)

When building the code with Xcode ("cmake -G Xcode"), there are 1000+
warnings about implicit 64 to 32 bit conversion.
This change adds a compile option to suppress such warnings when
generating an Xcode project.

Signed-off-by: Anton Dukhovnikov <antond@wetafx.co.nz>

src/cmake/compiler.cmake

@@ -148,6 +148,9 @@ if (CMAKE_COMPILER_IS_CLANG OR CMAKE_COMPILER_IS_APPLECLANG)
         # Don't warn about using unknown preprocessor symbols in `#if`
         add_compile_options ("-Wno-expansion-to-defined")
     endif ()
+    if (CMAKE_GENERATOR MATCHES "Xcode")
+        add_compile_options ("-Wno-shorten-64-to-32")
+    endif ()
 endif ()
 
 if (CMAKE_COMPILER_IS_GNUCC AND NOT (CMAKE_COMPILER_IS_CLANG OR CMAKE_COMPILER_IS_APPLECLANG))