memcpy needs to be in .text.memcpy

Summary: It was in .text, so the linker script couldn't place it,
and it was ending up outside the map-huge portion of the text section
of the binary.

Reviewed By: @ottoni

Differential Revision: D1744089

Signature: t1:1744089:1418774491:2dd29f46100159efed7a8fca64165c284a14f97e