Adjust compiler flag variables

In order to pass additional compiler flags while still keeping the required
flags intact (-pthread for example), we add a local set of flags on top of the
exsiting CFLAGS.

2019-01-11  Luis Machado  <luis.machado@linaro.org>

	* Test.mk (CFLAGS): Set to "-g -Wall"
	(FLAGS): New variable. Set to -pthread.
	Document variables.
	($(EXEC): Use FLAGS.

Signed-off-by: Luis Machado <luis.machado@linaro.org>
diff --git a/Test.mk b/Test.mk
index 3c12a9e..86e59ab 100644
--- a/Test.mk
+++ b/Test.mk
@@ -24,7 +24,14 @@
 SNT=$(wildcard *sanity.sh)
 TST=$(sort $(wildcard *[!{sanity}].sh))
 LOG=$(TST:.sh=.log)
-CFLAGS?=-g -Wall -pthread
+
+# Default flags passed to the compiler.
+CFLAGS?=-g -Wall
+
+# Required compiler flags to build the utils.
+FLAGS?=-pthread
+
+# Default compiler to build the utils.
 CC?=gcc
 
 # All utils' source files.
@@ -58,7 +65,7 @@
 
 # Target for building all the utils we need, from sources.
 $(EXEC): $(SRC)
-	$(CC) $(CFLAGS) $@.c -o $@
+	$(CC) $(CFLAGS) $(FLAGS) $@.c -o $@
 
 clean:
 	rm -f *.o $(EXEC)