Add support for mipsel #2029

Job	Run time
Checkout PDFium	3m 14s
Apply patches (linux, arm64, false)	16s
Apply patches (ios, arm64, false)	16s
Apply patches (linux, mipsel)	14s
Apply patches (linux, arm64, true)	16s
Apply patches (macos, arm64, true)	17s
Apply patches (android, arm64, false)	16s
Apply patches (ios, arm64, true)	21s
Apply patches (android, arm64, true)	25s
Apply patches (win, arm64, true)	15s
Apply patches (linux, ppc64)	20s
Apply patches (macos, arm64, false)	20s
Apply patches (linux, mips64el)	14s
Apply patches (win, arm64, false)	21s
Apply patches (emscripten, wasm)	16s
	7m 21s

Provide feedback