Avoid false positives on egl extension matching
Created by: agx
Due to the strstr prefix match EGL_EXT_foo would be incorrectly matched if EGL_EXT_foobar would be available but not foo.
This doesn't matter for the currently checked extensions but will matter for EGL_EXT_image_dma_buf_import_modifiers vs EGL_EXT_image_dma_buf_import
Code borrowed from weston