[SCSI] lpfc: fix problems with -Werror

Commit d38bd3aef ("Add -Werror compilation flag") is causing build breakage
with random gcc incarnations. These look like gcc problems, but we shouldn't
break the build because of a bad gcc. Fix this by adding a make flag

WARNINGS_BECOME_ERRORS=1

which is the same as aic7xxx uses so ordinarily the build doesn't use -Werror

Reported-by: Fengguang Wu <[e-mail]>
Cc: Alex Iannicelli <[e-mail]>
Cc: James Smart <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/lpfc/Makefile

···
 ccflags-$(GCOV) := -fprofile-arcs -ftest-coverage
 ccflags-$(GCOV) += -O0
 
+ifdef WARNINGS_BECOME_ERRORS
 ccflags-y += -Werror
+endif
 
 obj-$(CONFIG_SCSI_LPFC) := lpfc.o