build: Properly generate build dependency for autogenerated bitmap .h files
* bmp2rb generated a .h file that rockbox .c files used.
* .h files in .c files were used to generate dependency graphs for make
* When Make saw the .h file for the bitmap, it didn't know how what
to do with them
* Only arose in parallel builds
Fixed this by adding explicit dependencies for the .h files as part of
the existing 'bmpdepfile' function.
Solves the Xduoo X3 bootloader build failure that I could trigger 100%
of the time by using 'make -j8'
Change-Id: I6b3e78dde26c820a3b6c7c286e7d6c981b8e01fc
1 file changed