PC-BSD/trueos d8e1388sys/libkern strdup.c, sys/sys libkern.h

Add non-sleepable strdup variant strdup_flags

debugfs expects to do non-sleepable allocations

Reviewed by:    hps@
MFC after:      1 week
Sponsored by:   iX Systems
Differential Revision:  https://reviews.freebsd.org/D19259
DeltaFile
+11-2sys/libkern/strdup.c
+1-0sys/sys/libkern.h
+12-22 files

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