FreeBSD_HEAD - Build #3132 - Fixed

FreeBSD_HEAD - Build #3132 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD/3132/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD/3132/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD/3132/console

Change summaries:

287190 by marcel:
An error of -1 from parse_mount() indicates that the specification
was invalid. Don't trigger a mount failure (which by default means
a panic), but instead just move on to the next directive in the
configuration. This typically has us ask for the root mount.

PR:		163245

287189 by jhibbits:
Fix freescale sdhc driver, and add it to the files list.

Also, add it to the mmc DRIVER_MODULE attachment list.

287188 by jhibbits:
Use the macro definition for EXC_PGM_TRAP, instead of the magic number.

287187 by imp:
Make sys.mk more compatible with fmake by refraining from using :U
modifiers.

Differential Revision: https://reviews.freebsd.org/D3228