[makefile] Avoid using ?=

?= in a Makefile means that that variable can be overridden by the
environment.  This is confusing to users, especially with a generic
name like "ARCH".

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

src/Makefile

@@ -71,7 +71,7 @@ noargs : blib $(BIN)/NIC $(BIN)/gpxe.dsk $(BIN)/gpxe.iso $(BIN)/gpxe.usb $(BIN)/
 # If no architecture is specified in Config or on the command-line,
 # use that of the build machine.
 #
-ARCH		?= $(shell uname -m | sed -e s,i[3456789]86,i386,)
+ARCH		:= $(shell uname -m | sed -e s,i[3456789]86,i386,)
 
 # handle x86_64 like i386, but set -m32 option for 32bit code only
 ifeq ($(ARCH),x86_64)
@@ -98,7 +98,7 @@ LDFLAGS		+= $(EXTRA_LDFLAGS)
 
 # Embedded image, if present
 #
-EMBEDDED_IMAGE	?= /dev/null
+EMBEDDED_IMAGE	 = /dev/null
 
 ifneq ($(NO_WERROR),1)
 CFLAGS		+= -Werror

src/Makefile.housekeeping

@@ -58,16 +58,16 @@ ECHO_E_BIN_ECHO_TAB 	:= $(shell $(ECHO_E_BIN_ECHO) '\t')
 ECHO_E_BIN_ECHO_E_TAB 	:= $(shell $(ECHO_E_BIN_ECHO_E) '\t')
 
 ifeq ($(ECHO_E_ECHO_TAB),$(TAB))
-ECHO_E		?= $(ECHO_E_ECHO)
+ECHO_E		:= $(ECHO_E_ECHO)
 endif
 ifeq ($(ECHO_E_ECHO_E_TAB),$(TAB))
-ECHO_E		?= $(ECHO_E_ECHO_E)
+ECHO_E		:= $(ECHO_E_ECHO_E)
 endif
 ifeq ($(ECHO_E_BIN_ECHO_TAB),$(TAB))
-ECHO_E		?= $(ECHO_E_BIN_ECHO)
+ECHO_E		:= $(ECHO_E_BIN_ECHO)
 endif
 ifeq ($(ECHO_E_BIN_ECHO_E_TAB),$(TAB))
-ECHO_E		?= $(ECHO_E_BIN_ECHO_E)
+ECHO_E		:= $(ECHO_E_BIN_ECHO_E)
 endif
 
 .echocheck :