sys/modules: Make use of SRCS.${KERN_OPT}.

kmod.mk appends the value of SRCS.${KERN_OPT} for each defined kernel
option to SRCS.  This helper is shorter than appending to SRCS under
explicit checks on KERN_OPTS.

Reviewed by:	imp
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D38738

sys/modules/cxgbe/if_cxgbe/Makefile

@@ -23,9 +23,7 @@ SRCS+=	t4_filter.c
 SRCS+=	t4_hw.c
 SRCS+=	t4_if.c t4_if.h
 SRCS+=	t4_iov.c
-.if ${KERN_OPTS:MKERN_TLS} != ""
-SRCS+=	t6_kern_tls.c
-.endif
+SRCS.KERN_TLS+=	t6_kern_tls.c
 SRCS+=	t4_keyctx.c
 SRCS+=	t4_l2t.c
 SRCS+=	t4_main.c

sys/modules/geom/geom_uzip/Makefile

@@ -10,10 +10,8 @@ SRCS+=	g_uzip.h g_uzip_dapi.h g_uzip_lzma.h g_uzip_zlib.h g_uzip_softc.h \
     g_uzip_wrkthr.h
 
 # This works for buildkernel, but will disable zstd in geom_uzip out of tree.
-.if ${KERN_OPTS:MZSTDIO} != ""
-SRCS+=	g_uzip_zstd.c g_uzip_zstd.h
+SRCS.ZSTDIO+=	g_uzip_zstd.c g_uzip_zstd.h
 CFLAGS.g_uzip_zstd.c+=	-I${SRCTOP}/sys/contrib/zstd/lib/freebsd
-.endif
 
 #CFLAGS=	-g -DINVARIANT_SUPPORT -DINVARIANTS
 

sys/modules/vmm/Makefile

@@ -61,9 +61,7 @@ SRCS+=	vmcb.c		\
 	amdvi_hw.c	\
 	svm_msr.c
 
-.if ${KERN_OPTS:MBHYVE_SNAPSHOT} != ""
-SRCS+=	vmm_snapshot.c
-.endif
+SRCS.BHYVE_SNAPSHOT=	vmm_snapshot.c
 
 CLEANFILES=	vmx_assym.h vmx_genassym.o svm_assym.h svm_genassym.o