Allow cross-compilation.

makefile

@@ -5,8 +5,11 @@ help:
 
 ZIGOPTS ?=
 ZIGOPTIM ?= ReleaseSafe
+
+-include makefile.target
+
 build:
-	zig build -Doptimize=$(ZIGOPTIM) $(ZIGOPTS)
+	zig build -Doptimize=$(ZIGOPTIM) $(ZIGOPTS) $(TARGET_OPTION)
 
 PREFIX     ?= /usr/local
 LIBDIR     ?= $(PREFIX)/lib

makefile.target

@@ -0,0 +1,13 @@
+# This makefile include specific target options.
+
+TARGET ?=
+
+ifneq ($(TARGET),)
+	TARGET_OPTION=-Dtarget=$(TARGET)
+endif
+
+# In case the target is openbsd, and since the OpenBSD libc doesn't include a few system calls
+# used in any other zig compilation mode, we are forced to compile in ReleaseSmall.
+ifeq ($(TARGET),x86_64-openbsd)
+	ZIGOPTIM = ReleaseSmall
+endif