Update gwen/Projects/premake4.lua

targetsuffix appends the specified parameter to the end of the project name.
targetextension replaces the extension with the specified parameter.

The samples look for "gwen-staticd.lib", but if you use targetextension the only thing that is created is "gwen-staticd".

Without this fix the samples won't compile when set to debug mode.
Merge pull request #21 from pixellegacy/patch-1

Update gwen/Projects/premake4.lua