Makefile: remove SYSEXITS; auto-generate sysexits.h falling back to the template

Makefile

@@ -18,15 +18,13 @@ PREFIX ?= /usr/local
 
 MANDIR != [ $(PREFIX) = / ] && printf '/usr/share/man\n' \
 	|| printf '/share/man\n'
-SYSEXITS != cpp -M -include sysexits.h /dev/null | tr ' ' '\n' \
-	| sed -n 's/sysexits\.h//p' || printf 'include\n'
 
 CC ?= cc
 RUSTC ?= rustc
 RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 	--extern sysexits=build/o/libsysexits.rlib \
 	--extern strerror=build/o/libstrerror.rlib
-CFLAGS += -I$(SYSEXITS)
+CFLAGS += -Ibuild/include
 
 .PHONY: all
 all: docs dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
@@ -65,6 +63,12 @@ docs: docs/ build
 rustlibs: build/o/libsysexits.rlib build/o/libgetopt.rlib \
 	build/o/libstrerror.rlib
 
+build/include/sysexits.h: build
+	cpp -dM -include sysexits.h /dev/null \
+			| grep '^.define EX_' >$@ \
+		|| cpp -dM -include stdlib.h include/sysexits.h.template \
+			| grep -e '^.define EX_' -e '^.define EXIT_' >$@
+
 build/o/libgetopt.rlib: build src/getopt-rs/lib.rs
 	$(RUSTC) $(RUSTFLAGS) --crate-type=lib --crate-name=getopt \
 		-o $@ src/getopt-rs/lib.rs
@@ -74,9 +78,7 @@ build/o/libstrerror.rlib: build src/strerror.rs
 		src/strerror.rs
 
 # bandage solution until bindgen(1) gets stdin support
-build/o/libsysexits.rlib: build $(SYSEXITS)sysexits.h
-	printf '\043define EXIT_FAILURE 1\n' | cat - $(SYSEXITS)sysexits.h \
-		> build/include/sysexits.h 
+build/o/libsysexits.rlib: build build/include/sysexits.h
 	bindgen --default-macro-constant-type signed --use-core --formatter=none \
 		build/include/sysexits.h | $(RUSTC) $(RUSTFLAGS) --crate-type lib -o $@ -