"make debug=t" enables debuginfo again

...which had inadvertently been broken with
99db9f22 "Make --enable-symbols orthogonal to
--enable-debug/-dbgutil"

Change-Id: I3962aa8c67426f3aebc5ad746f7ac281c68d941a

solenv/gbuild/gbuild.mk

@@ -87,12 +87,14 @@ gb_DEBUGLEVEL := 1
 # make DEBUG=true should force -g
 ifeq ($(origin DEBUG),command line)
 ENABLE_DEBUGINFO_FOR := all
+ENABLE_SYMBOLS := TRUE
 endif
 endif
 ifneq ($(strip $(debug)),)
 gb_DEBUGLEVEL := 1
 ifeq ($(origin debug),command line)
 ENABLE_DEBUGINFO_FOR := all
+ENABLE_SYMBOLS := TRUE
 endif
 endif
 ifeq ($(gb_ENABLE_DBGUTIL),$(true))