Automatically distinguish pkgsrc and homebrew systems,

always stop on compiler warning.

Makefile

@@ -3,15 +3,19 @@
 #
 
 CC  = clang
+CFLAGS += -Wall -Wextra -Werror
 OS != uname
 
 UMASK = 77
 
 .if ${OS}   == Darwin
     GROUP = _www
-    # CFLAGS += -I/opt/pkg/include/mysql -L/opt/pkg/lib      # pkgsrc
+.if exists (/opt/pkg/include/mysql)
+    CFLAGS += -I/opt/pkg/include/mysql -L/opt/pkg/lib        # pkgsrc
+.else
     CFLAGS += -I/usr/local/Cellar/mysql/5.7.21/include/mysql # homebrew
     CFLAGS += -L/usr/local/Cellar/mysql/5.7.21/lib           # homebrew
+.endif
 .elif ${OS} == FreeBSD
     GROUP = www
     CFLAGS += -I/usr/local/include/mysql -L/usr/local/lib/mysql
@@ -29,19 +33,19 @@ all: mysql-test
 
 mysql: mysql-test
 
-mysql-test: mysql-test.c
+mysql-test! mysql-test.c
 	umask ${UMASK} && ${CC} ${CFLAGS} ${LIBS} -D__MYSQL__ -o $@ $<
 	chmod 600 $<
 	chmod 710 $@
-	chgrp ${GROUP} $@
+	-chgrp ${GROUP} $@
 
 galera: galera-test
 
-galera-test: galera-test.c
+galera-test! galera-test.c
 	umask ${UMASK} && ${CC} ${CFLAGS} ${LIBS} -D__GALERA__ -o $@ $<
 	chmod 600 $<
 	chmod 710 $@
-	chgrp ${GROUP} $@
+	-chgrp ${GROUP} $@
 
 .PHONY: clean clean-mysql clean-galera