build: unify verbosity handling

This change introduces a few helper variables for dealing with verbose
and silent build modes: `silent`, `verbose`, `q` and `s`.

The `silent` and `verbose` variables are boolean values determining
whether the build system has been configured to run silently or
verbosely respectively (i.e. with `--silent` or `V=1`).

These two modes cannot be used together - if `silent` is truthy then
`verbose` is always falsy. As such:

    make --silent V=1

... results in a silent build.

In addition to these boolean variables, we also introduce two new
variables - `s` and `q` - for use in rule recipes to conditionally
suppress the output of commands.

When building silently, `s` expands to a value which disables the
command that follows, and `q` expands to a value which supppresses
echoing of the command:

    $(s)echo 'This command is neither echoed nor executed'
    $(q)echo 'This command is executed but not echoed'

When building verbosely, `s` expands to a value which disables the
command that follows, and `q` expands to nothing:

    $(s)echo 'This command is neither echoed nor executed'
    $(q)echo 'This command is executed and echoed'

In all other cases, both `s` and `q` expand to a value which suppresses
echoing of the command that follows:

    $(s)echo 'This command is executed but not echoed'
    $(q)echo 'This command is executed but not echoed'

The `s` variable is predominantly useful for `echo` commands, where you
always want to suppress echoing of the command itself, whilst `q` is
more useful for all other commands.

Change-Id: I8d8ff6ed714d3cb401946c52955887ed7dca602b
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/tools/sptool/Makefile b/tools/sptool/Makefile
index a913ce5..e336a0c 100644
--- a/tools/sptool/Makefile
+++ b/tools/sptool/Makefile
@@ -9,12 +9,12 @@
 MAKE_HELPERS_DIRECTORY := ../../make_helpers/
 include ${MAKE_HELPERS_DIRECTORY}build_macros.mk
 include ${MAKE_HELPERS_DIRECTORY}build_env.mk
+include ${MAKE_HELPERS_DIRECTORY}common.mk
 include ${MAKE_HELPERS_DIRECTORY}toolchain.mk
 
 SPTOOL  ?= sptool${BIN_EXT}
 PROJECT := $(notdir ${SPTOOL})
 OBJECTS := sptool.o
-V ?= 0
 
 override CPPFLAGS += -D_GNU_SOURCE -D_XOPEN_SOURCE=700
 HOSTCCFLAGS := -Wall -Werror -pedantic -std=c99
@@ -24,12 +24,6 @@
   HOSTCCFLAGS += -O2
 endif
 
-ifeq (${V},0)
-  Q := @
-else
-  Q :=
-endif
-
 INCLUDE_PATHS := -I../../include/tools_share
 
 .PHONY: all clean distclean
@@ -37,15 +31,15 @@
 all: ${PROJECT}
 
 ${PROJECT}: ${OBJECTS} Makefile
-	@echo "  HOSTLD  $@"
-	${Q}$(host-cc) ${OBJECTS} -o $@ ${LDLIBS}
-	@${ECHO_BLANK_LINE}
-	@echo "Built $@ successfully"
-	@${ECHO_BLANK_LINE}
+	$(s)echo "  HOSTLD  $@"
+	$(q)$(host-cc) ${OBJECTS} -o $@ ${LDLIBS}
+	$(s)echo
+	$(s)echo "Built $@ successfully"
+	$(s)echo
 
 %.o: %.c Makefile
-	@echo "  HOSTCC  $<"
-	${Q}$(host-cc) -c ${CPPFLAGS} ${HOSTCCFLAGS} ${INCLUDE_PATHS} $< -o $@
+	$(s)echo "  HOSTCC  $<"
+	$(q)$(host-cc) -c ${CPPFLAGS} ${HOSTCCFLAGS} ${INCLUDE_PATHS} $< -o $@
 
 clean:
 	$(call SHELL_DELETE_ALL, ${PROJECT} ${OBJECTS})