Enables generating Lua's pkg-config file.

http://lua-users.org/lists/lua-l/2015-03/msg00338.html

--- a/Makefile	2016-08-16 19:44:27.363614964 +0200
+++ b/Makefile	2016-08-16 19:49:22.623070005 +0200
@@ -13,6 +13,7 @@
 INSTALL_BIN= $(INSTALL_TOP)/bin
 INSTALL_INC= $(INSTALL_TOP)/include
 INSTALL_LIB= $(INSTALL_TOP)/lib
+INSTALL_PC= $(INSTALL_LIB)/pkgconfig
 INSTALL_MAN= $(INSTALL_TOP)/man/man1
 #
 # You probably want to make INSTALL_LMOD and INSTALL_CMOD consistent with
@@ -41,9 +42,12 @@
 PLATS= aix ansi bsd freebsd generic linux macosx mingw posix solaris
 
 # What to install.
-TO_BIN= lua luac
+INTERPRETER= lua
+COMPILER= luac
+TO_BIN= $(INTERPRETER) $(COMPILER)
 TO_INC= lua.h luaconf.h lualib.h lauxlib.h ../etc/lua.hpp
 TO_LIB= liblua.a liblua.so liblua.so.${V}
+TO_PC= lua-$(V).pc
 TO_MAN= lua.1 luac.1
 
 # Lua version and release.
@@ -52,17 +56,22 @@
 
 all:	$(PLAT)
 
-$(PLATS) clean:
+$(PLATS):
 	cd src && $(MAKE) $@ V=$(V) R=$(R)
 
+clean:
+	cd src && $(MAKE) $@
+	$(RM) $(TO_PC)
+
 test:	dummy
 	src/lua test/hello.lua
 
-install: dummy
-	cd src && $(MKDIR) $(INSTALL_BIN) $(INSTALL_INC) $(INSTALL_LIB) $(INSTALL_MAN) $(INSTALL_LMOD) $(INSTALL_CMOD)
+install: dummy $(TO_PC)
+	cd src && $(MKDIR) $(INSTALL_BIN) $(INSTALL_INC) $(INSTALL_LIB) $(INSTALL_PC) $(INSTALL_MAN) $(INSTALL_LMOD) $(INSTALL_CMOD)
 	cd src && $(INSTALL_EXEC) $(TO_BIN) $(INSTALL_BIN)
 	cd src && $(INSTALL_DATA) $(TO_INC) $(INSTALL_INC)
 	cd src && $(INSTALL_DATA) $(TO_LIB) $(INSTALL_LIB)
+	cd src && $(INSTALL_DATA) ../$(TO_PC) $(INSTALL_PC)
 	cd doc && $(INSTALL_DATA) $(TO_MAN) $(INSTALL_MAN)
 
 ranlib:
@@ -95,6 +104,7 @@
 	@echo "INSTALL_BIN = $(INSTALL_BIN)"
 	@echo "INSTALL_INC = $(INSTALL_INC)"
 	@echo "INSTALL_LIB = $(INSTALL_LIB)"
+	@echo "INSTALL_PC = $(INSTALL_PC)"
 	@echo "INSTALL_MAN = $(INSTALL_MAN)"
 	@echo "INSTALL_LMOD = $(INSTALL_LMOD)"
 	@echo "INSTALL_CMOD = $(INSTALL_CMOD)"
@@ -111,6 +121,7 @@
 	@echo "TO_BIN = $(TO_BIN)"
 	@echo "TO_INC = $(TO_INC)"
 	@echo "TO_LIB = $(TO_LIB)"
+	@echo "TO_PC = $(TO_PC)"
 	@echo "TO_MAN = $(TO_MAN)"
 
 # echo config parameters as Lua code
@@ -122,7 +133,29 @@
 	@$(MAKE) echo | grep = | sed -e 's/= /= "/' -e 's/$$/"/' #-e 's/""/nil/'
 	@echo "-- EOF"
 
+pc:
+	@echo 'prefix=$(INSTALL_TOP)'
+	@echo 'libdir=$(INSTALL_LIB)'
+	@echo 'includedir=$(INSTALL_INC)'
+	@echo 'bindir=$(INSTALL_BIN)'
+	@echo
+	@echo 'INSTALL_LMOD=$(INSTALL_LMOD)'
+	@echo 'INSTALL_CMOD=$(INSTALL_CMOD)'
+	@echo 'INTERPRETER=$${bindir}/$(INTERPRETER)'
+	@echo 'COMPILER=$${bindir}/$(COMPILER)'
+	@echo
+	@echo 'Name: Lua'
+	@echo 'Description: A powerful, fast, lightweight, embeddable scripting language'
+	@echo 'Version: $(R)'
+	@echo
+	@echo 'Libs: -L$${libdir} -llua -lm'
+	@echo 'Cflags: -I$${includedir}'
+
+pkg-config: $(TO_PC)
+$(TO_PC):
+	@$(MAKE) -s pc > $@
+
 # list targets that do not create files (but not all makes understand .PHONY)
-.PHONY: all $(PLATS) clean test install local none dummy echo pecho lecho
+.PHONY: all $(PLATS) clean test install local none dummy echo pecho lecho pkg-config
 
 # (end of Makefile)