Define several extra macros in bsd.sys.mk and sys/conf/kern.pre.mk, to

get rid of testing explicitly for clang (using ${CC:T:Mclang}) in
individual Makefiles.

Instead, use the following extra macros, for use with clang:
- NO_WERROR.clang       (disables -Werror)
- NO_WCAST_ALIGN.clang  (disables -Wcast-align)
- NO_WFORMAT.clang	(disables -Wformat and friends)
- CLANG_NO_IAS		(disables integrated assembler)
- CLANG_OPT_SMALL	(adds flags for extra small size optimizations)

As a side effect, this enables setting CC/CXX/CPP in src.conf instead of
make.conf!  For clang, use the following:

CC=clang
CXX=clang++
CPP=clang-cpp

MFC after:	2 weeks

2 files changed, 2 insertions, 6 deletions

diff --git a/usr.bin/netstat/Makefile b/usr.bin/netstat/Makefile
index 3f7fe9f..224f2b7 100644
--- a/usr.bin/netstat/Makefile
+++ b/usr.bin/netstat/Makefile
@@ -8,11 +8,9 @@ SRCS=	if.c inet.c main.c mbuf.c mroute.c netisr.c route.c \
 	unix.c atalk.c mroute6.c ipsec.c bpf.c pfkey.c sctp.c
 
 WARNS?=	3
-.if ${CC:T:Mclang} == "clang"
 # XXX: Work around a clang false positive with format string warnings
 # and ntohs macros (see LLVM PR 11313).
-NO_WFORMAT=
-.endif
+NO_WFORMAT.clang=
 CFLAGS+=-fno-strict-aliasing
 
 CFLAGS+=-DIPSEC
diff --git a/usr.bin/vacation/Makefile b/usr.bin/vacation/Makefile
index 2b13a28..ad77dba 100644
--- a/usr.bin/vacation/Makefile
+++ b/usr.bin/vacation/Makefile
@@ -11,12 +11,10 @@ CFLAGS+=-D_FFR_LISTDB -D_FFR_DEBUG
 
 WARNS?=	2
 
-.if ${CC:T:Mclang} == "clang"
 # Unfortunately, clang gives warnings about sendmail code that cannot
 # be turned off yet.  Since this is contrib code, and we don't really
 # care about the warnings, just make them non-fatal for now.
-NO_WERROR=
-.endif
+NO_WERROR.clang=
 
 LIBSMDIR=	${.OBJDIR}/../../lib/libsm
 LIBSM=		${LIBSMDIR}/libsm.a