Makefile: adapt targets to the OS

The Listener is built only on Linux, the Positioner is not built on
OpenBSD. Some other changes might be required.

In common.mk, the OS is forced to Linux if we build for OpenWrt, which
should allow to cross-compile from BSD systems.

Makefile

@@ -25,18 +25,24 @@ include common.mk
 
 ## Compilation ##
 
-all: \
-	c \
-	owlps-positioner
-
-c: \
+C_TARGETS := \
 	libowlps \
 	libowlps-client \
 	libowlps-resultreader \
 	owlps-client \
-	owlps-listener \
 	owlps-aggregator \
 	owlps-udp-to-http
+ifeq "$(OS)" "Linux"
+	C_TARGETS += owlps-listener
+endif
+
+ALL_TARGETS := $(C_TARGETS)
+ifneq "$(OS)" "OpenBSD"
+	ALL_TARGETS += owlps-positioner
+endif
+
+all: $(ALL_TARGETS)
+c: $(C_TARGETS)
 
 libowlps:
 	@$(MAKE) -C $@ $(ARG)

common.mk

@@ -91,6 +91,9 @@ CFLAGS :=
 CXXFLAGS :=
 LDFLAGS :=
 
+# OS detection
+OS := $(shell uname)
+
 ## OpenWrt specifics ##
 #
 # To compile for OpenWrt, the OPENWRT_VERSION variable must be set.
@@ -121,6 +124,8 @@ ifndef OPENWRT_TARGET
 	OPENWRT_TARGET := atheros
 endif
 ifdef OPENWRT_VERSION
+	OS := Linux
+
 	TOOLCHAIN_PREFIX := $(OPENWRT_ROOT)/$(OPENWRT_TARGET)/$(OPENWRT_VERSION)
 	STAGING_DIR := $(TOOLCHAIN_PREFIX)/staging_dir
 	TOOLCHAIN1 := $(TOOLCHAIN_PREFIX)/toolchain_gcc_uClibc
@@ -160,7 +165,6 @@ CFLAGS += -D DEBUG
 #STRIPFLAGS += -Wl,-s
 
 # OS specific flags
-OS := $(shell uname)
 ifeq "$(OS)" "DragonFly"
 	CFLAGS += -I/usr/pkg/include
 	LDFLAGS += -L/usr/pkg/lib