Add a mechanism to allow Makefiles to specify the particular C dialect

in which the source code is written.  This is controlled by the CSTD
variable, which can have one of the following values:

  - "k&r"		=> -traditional
  - "c89" or "c90"	=> -std=iso9899:1990
  - "c94" or "c95"	=> -std=iso9899:199409
  - "c99"		=> -std=iso9899:1999

The corresponding option is added to CFLAGS regardless of WARNS level.
This also removes -ansi from WARNS level 6, but adds -Wno-long-long to
work around a weird gcc bug (-ansi, which is supposedly equivalent to
-std=iso9899:1990, seems to turn long long warnings off instead of on)

If CSTD is undefined, CFLAGS are unchanged except for the -ansi /
-Wno-long-long change mentioned above for WARNS level 6.

share/mk/bsd.sys.mk

@@ -9,6 +9,17 @@
 # for GCC:  http://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_3.html#IDX143
 
 .if !defined(NO_WARNS)
+. if defined(CSTD)
+.  if ${CSTD} == "k&r"
+CFLAGS          += -traditional
+.  elif ${CSTD} == "c89" || ${CSTD} == "c90"
+CFLAGS          += -std=iso9899:1990
+.  elif ${CSTD} == "c94" || ${CSTD} == "c95"
+CFLAGS          += -std=iso9899:199409
+.  elif ${CSTD} == "c99"
+CFLAGS          += -std=iso9899:1999
+.  endif
+. endif
 . if defined(WARNS)
 .  if ${WARNS} > 0
 CFLAGS		+=	-Wsystem-headers
@@ -27,7 +38,7 @@ CFLAGS		+=	-Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wcast-al
 .  endif
 # BDECFLAGS
 .  if ${WARNS} > 5
-CFLAGS		+=	-ansi -pedantic -Wbad-function-cast -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls
+CFLAGS		+=	-pedantic -Wno-long-long -Wbad-function-cast -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls
 .  endif
 .  if ${WARNS} > 1 && ${WARNS} < 5
 # XXX Delete -Wuninitialized by default for now -- the compiler doesn't