incdep.c: deal with pairfait dep files

[bird]

Must be able to handle the multi dependency target declarations like this:

/sol-parfait/out/solaris.amd64/release/obj/RuntimeR3/common/alloc/alloc.o.bc \
  /sol-parfait/out/solaris.amd64/release/obj/RuntimeR3/common/alloc/alloc.o: \
  /sol-parfait/src/VBox/Runtime/common/alloc/alloc.cpp \
  /sol-parfait/include/iprt/mem.h \
  /sol-parfait/include/iprt/cdefs.h \
  /sol-parfait/include/iprt/types.h \
  /sol-parfait/include/iprt/stdint.h \
  /usr/include/stdint.h /usr/include/sys/stdint.h \
  /usr/include/sys/int_types.h /usr/include/sys/feature_tests.h \
  /usr/include/sys/ccompile.h /usr/include/sys/isa_defs.h \
  /usr/include/sys/int_limits.h /usr/include/sys/int_const.h \
  /usr/include/stddef.h /usr/include/iso/stddef_iso.h \
  /usr/include/sys/types.h /usr/include/sys/machtypes.h \
  /usr/include/ia32/sys/machtypes.h /usr/include/sys/select.h \
  /usr/include/sys/time_impl.h /usr/include/sys/time.h \
  /usr/include/time.h /usr/include/iso/time_iso.h \
  /sol-parfait/src/VBox/Runtime/include/internal/iprt.h \
  /sol-parfait/include/iprt/assert.h \
  /sol-parfait/include/iprt/stdarg.h \
  /usr/sfw/lib/gcc/i386-pc-solaris2.11/3.4.3/include/stdarg.h \
  /sol-parfait/include/iprt/string.h \
  /sol-parfait/include/iprt/err.h /usr/include/string.h \
  /usr/include/iso/string_iso.h