Fix cast for clang/clang++ in -c++17 mode, using a C-style cast so it's buildable by plain C users.

Add Makefile.clang
Add regression test for Travis

[#39]

c/common/i2cdriver.c

@@ -323,7 +323,7 @@ uint8_t i2c_reset(I2CDriver *sd)
 
 int i2c_start(I2CDriver *sd, uint8_t dev, uint8_t op)
 {
-  uint8_t start[2] = {'s', (dev << 1) | op};
+  uint8_t start[2] = {'s', (uint8_t)((dev << 1) | op)};
   writeToSerialPort(sd->port, start, sizeof(start));
   return i2c_ack(sd);
 }

c/linux/Makefile.clang

@@ -0,0 +1,11 @@
+CC=clang
+CFLAGS += -I common -Wall -Wpointer-sign -xc++ -std=c++17 # -Werror
+
+all: build/i2ccl
+
+install: all
+	cp build/i2ccl /usr/local/bin
+
+build/i2ccl: linux/i2c.c common/i2cdriver.c
+	mkdir -p build/
+	$(CC) -o $@ $(CPPFLAGS) $(CFLAGS) $^

testall

@@ -14,3 +14,4 @@ python -c 'from i2cdriver import I2CDriver'
 
 cd c
 make -f linux/Makefile
+make -f linux/Makefile.clang