Refresh EGL header to work with the NDK

This change allows to use this header with the NDK's standalone toolchain.
For the record, the NDK toolchain defines __ANDROID__ as a compiler built-in
macro, this is however not the case currently for the prebuilt binaries that
are being used by the full Android build system, which otherwise defines ANDROID.

This change allows the header to be used by all toolchains properly. Note however
that we should properly should change our toolchain and sources to provide and
rely on __ANDROID__ instead of ANDROID though.

Change-Id: Iaa1aa1146985b5f24dcf3a83d9ddb9b4b59dc328