Remove duplication and centralize testing of various config(8)ed features.

sys/conf/Makefile.amd64

@@ -31,9 +31,6 @@ S=	../../..
 .endif
 .include "$S/conf/kern.pre.mk"
 
-DDB_ENABLED!=	grep DDB opt_ddb.h || true ; echo
-DTR_ENABLED!=	grep KDTRACE_FRAME opt_kdtrace.h || true ; echo
-HWPMC_ENABLED!=	grep HWPMC opt_hwpmc_hooks.h || true ; echo
 .if !empty(DDB_ENABLED) || !empty(DTR_ENABLED) || !empty(HWPMC_ENABLED)
 CFLAGS+=	-fno-omit-frame-pointer
 .endif

sys/conf/Makefile.arm

@@ -39,8 +39,6 @@ SYSTEM_DEP:= ${SYSTEM_DEP:$S/conf/ldscript.$M=ldscript.$M}
 STRIP_FLAGS = -S
 .endif
 
-DDB_ENABLED!=	grep DDB opt_ddb.h || true ; echo
-
 .if empty(DDB_ENABLED)
 CFLAGS += -mno-apcs-frame
 .endif

sys/conf/Makefile.powerpc

@@ -37,7 +37,6 @@ INCLUDES+= -I$S/contrib/libfdt
 
 CFLAGS+= -msoft-float -Wa,-many
 
-DDB_ENABLED!=	grep DDB opt_ddb.h || true ; echo
 .if !empty(DDB_ENABLED)
 CFLAGS+=	-fno-omit-frame-pointer
 .endif

sys/conf/kern.pre.mk

@@ -189,3 +189,8 @@ MKMODULESENV+=	WITHOUT_MODULES="${WITHOUT_MODULES}"
 .if defined(DEBUG)
 MKMODULESENV+=	DEBUG_FLAGS="${DEBUG}"
 .endif
+
+# Are various things configured?
+DDB_ENABLED!=	grep DDB opt_ddb.h || true ; echo
+DTR_ENABLED!=	grep KDTRACE_FRAME opt_kdtrace.h || true ; echo
+HWPMC_ENABLED!=	grep HWPMC opt_hwpmc_hooks.h || true ; echo