simplify top-level Makefile some more

Change-Id: Ie1d53db34f812a83940196d0bf6e4ad8aaa8eab6

Makefile.in

@@ -9,9 +9,7 @@
 
 .PHONY : all bootstrap gbuild build build-non-l10n-only build-l10n-only check clean clean-build clean-host test-install distclean distro-pack-install docs download fetch findunusedcode get-submodules id install install-strip subsequentcheck tags debugrun help slowcheck translations unitcheck
 
-ifeq ($(MAKECMDGOALS),)
-MAKECMDGOALS:=all
-endif
+MAKECMDGOALS?=all
 
 SHELL=/usr/bin/env bash
 SRCDIR := @SRC_ROOT@
@@ -47,19 +45,11 @@ else # MAKE_RESTARTS
 
 all: build
 
-ifeq ($(gb_Side),)
-gb_Side := host
-endif
+gb_Side ?= host
 
 include $(BUILDDIR)/config_$(gb_Side).mk
 
-ifeq ($(GMAKE_OPTIONS),)
-ifeq ($(verbose)$(VERBOSE),)
-export GMAKE_OPTIONS:=-rs$(MAKEFLAGS)
-else
-export GMAKE_OPTIONS:=-r$(MAKEFLAGS)
-endif
-endif
+export GMAKE_OPTIONS?=-r$(if $(verbose)$(VERBOSE),,s)$(MAKEFLAGS)
 
 #
 # Partial Build