make: Use predefined variables in rules.

makefile

@@ -1,5 +1,9 @@
 prefix=/usr/local
 
+CFLAGS += -Wall
+CXXFLAGS += -D_GLIBCXX_DEBUG -std=c++11 -Wall -Werror -fmax-errors=5
+LDLIBS += -lm
+
 ifeq ($(findstring armv6,$(shell uname -m)),armv6)
 # Broadcom BCM2835 SoC with 700 MHz 32-bit ARM 1176JZF-S (ARMv6 arch)
 PI_VERSION = -DRPI1
@@ -12,16 +16,16 @@ endif
 all: wspr gpioclk
 
 mailbox.o: mailbox.c mailbox.h
-	g++ -c -Wall -lm mailbox.c
+	$(CC) $(CFLAGS) -c mailbox.c
 
 wspr: mailbox.o wspr.cpp mailbox.h
-	g++ -D_GLIBCXX_DEBUG -std=c++11 -Wall -Werror -fmax-errors=5 -lm $(PI_VERSION) mailbox.o wspr.cpp -owspr
+	$(CXX) $(CXXFLAGS) $(LDFLAGS) $(LDLIBS) $(PI_VERSION) mailbox.o wspr.cpp -owspr
 
 gpioclk: gpioclk.cpp
-	g++ -D_GLIBCXX_DEBUG -std=c++11 -Wall -Werror -fmax-errors=5 -lm $(PI_VERSION) gpioclk.cpp -ogpioclk
+	$(CXX) $(CXXFLAGS) $(LDFLAGS) $(LDLIBS) $(PI_VERSION) gpioclk.cpp -ogpioclk
 
 clean:
-	-rm -f gpioclk gpioclk.o wspr wspr.o mailbox.o
+	$(RM) *.o gpioclk wspr
 
 .PHONY: install
 install: wspr
@@ -30,6 +34,5 @@ install: wspr
 
 .PHONY: uninstall
 uninstall:
-	-rm -f $(prefix)/bin/wspr
-	-rm -f $(prefix)/bin/gpioclk
+	$(RM) $(prefix)/bin/wspr $(prefix)/bin/gpioclk
 

wspr.cpp

@@ -45,7 +45,12 @@
 #include <pthread.h>
 #include <sys/timex.h>
 
+#ifdef __cplusplus
+extern "C" {
 #include "mailbox.h"
+}
+#endif /* __cplusplus */
+
 
 // Note on accessing memory in RPi:
 //