Building for PHP
libvpx sources https://github.com/winlibs/libvpx
Common tools used to compile PHP
To compile libxpm the VS projects have to be generated first, follow the instructions under the libvpx project page. PHP uses the static libvpx linked with the static VC runtime. Note that the VS project files are generated with make under Cygwin and empirically the paths in the project files are often Cygwin paths, so they might need correction.
Open in the generated vpx.sln solution in visual studio and compile the vpx project.