Fix compilation on various *nix systems

Unfortunately this breaks support for BSD make.

Makefile

@@ -46,7 +46,7 @@ dist: clean
 
 install: vis
 	@echo stripping executable
-	@strip -s vis
+	@${STRIP} vis
 	@echo installing executable file to ${DESTDIR}${PREFIX}/bin
 	@mkdir -p ${DESTDIR}${PREFIX}/bin
 	@cp -f vis ${DESTDIR}${PREFIX}/bin

config.mk

@@ -3,16 +3,33 @@ VERSION = devel
 
 # Customize below to fit your system
 
-PREFIX = /usr/local
+PREFIX ?= /usr/local
 MANPREFIX = ${PREFIX}/share/man
 
 INCS = -I.
 LIBS = -lc -lncursesw
 
+ifeq ($(shell uname),Darwin)
+	LIBS = -lc -lncurses
+	CFLAGS += -D_DARWIN_C_SOURCE
+else ifeq ($(shell uname),OpenBSD)
+	CFLAGS += -D_BSD_SOURCE
+else ifeq ($(shell uname),FreeBSD)
+	CFLAGS += -D_BSD_SOURCE
+else ifeq ($(shell uname),NetBSD)
+	LIBS = -lc -lcurses
+	CFLAGS += -D_BSD_SOURCE
+else ifeq ($(shell uname),SunOS)
+	INCS += -I/usr/include/ncurses
+else ifeq ($(shell uname),AIX)
+	CFLAGS += -D_ALL_SOURCE
+endif
+
 CFLAGS += -std=c99 -Os ${INCS} -DVERSION=\"${VERSION}\" -DNDEBUG -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700
 
 LDFLAGS += ${LIBS}
 
 DEBUG_CFLAGS = ${CFLAGS} -UNDEBUG -O0 -g -ggdb -Wall -Wextra -Wno-missing-field-initializers -Wno-unused-parameter
 
-CC = cc
+CC ?= cc
+STRIP ?= strip