build(win32): Fix SafeSEH build on Win32

[jan-auer]

When building with enabled Safe SEH on Windows x86, linking failed with the following error:

error LNK2026: module unsafe for SAFESEH image

This is due to a missing compile flag to cl when building MASM modules for crashpad_util. Crashpad sets this by adding /safeseh to ASM options. In premake, this is possible by setting exceptionhandling 'SEH' on ASM files for the Win32 platform. It took me a little to find the correct filter, but now it generates this in the VS project XML (which builds fine):

<Masm Include="..\crashpad\build\crashpad\util\misc\capture_context_win.asm">
  <UseSafeExceptionHandlers Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">true</UseSafeExceptionHandlers>
  <UseSafeExceptionHandlers Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</UseSafeExceptionHandlers>
</Masm>

Fixes #56