This gets rid of a bunch of "strerror(errno)" bits.
Will convert fuse.cpp after
https://android-review.googlesource.com/#/c/247780 lands.
Bug: 30110940
Change-Id: Iacefe5b6519b217ed687c709763fe5827b3b0b59
sdcard.c is a *really* big file. This makes it hard to do things like
improving priv dropping or adding more sandboxing. Extract all
FUSE-related code to a separate unit, fuse.{h|c}, which exports only
two functions. Convert the rest of sdcard.c to C++ as sdcard.cpp.
fuse.c is kept as C (at least for now) since interacting with the FUSE
API is realistically easier from C.
Bug: 30110940
Change-Id: I188bfdc21c184742117e07539adb09090d4d747c
