fmap.h: Add `extern "C"` to make it compatible to C++.

fmap.h is a C header file. We add `extern "C"` to let C++ code be able
to include it.

TEST=emerge flashmap
     successfully build a c++ program which includes fmap.h

Change-Id: I0317ddc9ce7182d69899d7756688ee7dcaded26a
Commit-Ready: Nicolas Boichat <>
Tested-by: Chih-Yu Huang <>
Reviewed-by: Mike Frysinger <>
1 file changed