[clutter/windows-fixes: 2/4] examples: Define _USE_MATH_DEFINES as needed

[Chun-wei Fan <fanchunwei src gnome org>]

commit b377845cf3bb07c9296db779311db978876d0b4b
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed Oct 20 11:03:45 2021 +0800

    examples: Define _USE_MATH_DEFINES as needed
    
    For builds using the Visual Studio headers, we must define
    _USE_MATH_DEFINES in order for _M_PI to work.

 examples/meson.build | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/examples/meson.build b/examples/meson.build
index 532e9bb21..256168945 100644
--- a/examples/meson.build
+++ b/examples/meson.build
@@ -32,10 +32,17 @@ if enable_pixbuf_tests
   ]
 endif
 
+examples_cargs = []
+
+if cc.get_argument_syntax() == 'msvc'
+  examples_cargs += '-D_USE_MATH_DEFINES'
+endif
+
 foreach e: examples
   executable(
     e,
     e + '.c',
     dependencies: examples_deps,
+    c_args: examples_cargs,
   )
 endforeach