From: Jakub Jirutka <jakub@jirutka.cz>

Fix Makefile to respect system CFLAGS, LDFLAGS, and CC provided by environment.
Allow to specify pkg-config command using variable, to be friendly with
cross-compiling etc.

diff --git a/Makefile b/Makefile
index 195ef6b..375fb65 100644
--- a/Makefile
+++ b/Makefile
@@ -2,9 +2,10 @@ T=openssl
 
 PREFIX		?=/usr/local
 LIB_OPTION	?= -shared 
+PKG_CONFIG	?= pkg-config
 
 #Lua auto detect
-LUA_VERSION ?= $(shell pkg-config luajit --print-provides)
+LUA_VERSION ?= $(shell $(PKG_CONFIG) luajit --print-provides)
 ifeq ($(LUA_VERSION),)                         ############ Not use luajit
 LUAV		?= $(shell lua -e "_,_,v=string.find(_VERSION,'Lua (.+)');print(v)")
 LUA_CFLAGS	?= -I$(PREFIX)/include/lua$(LUAV)
@@ -12,8 +13,8 @@ LUA_LIBS	?= -L$(PREFIX)/lib
 LUA_LIBDIR	?= $(PREFIX)/lib/lua/$(LUAV)
 else
 LUAV		?= $(shell lua -e "_,_,v=string.find(_VERSION,'Lua (.+)');print(v)")
-LUA_CFLAGS	?= $(shell pkg-config luajit --cflags)
-LUA_LIBS	?= $(shell pkg-config luajit --libs)
+LUA_CFLAGS	?= $(shell $(PKG_CONFIG) luajit --cflags)
+LUA_LIBS	?= $(shell $(PKG_CONFIG) luajit --libs)
 LUA_LIBDIR	?= $(PREFIX)/lib/lua/$(LUAV)
 endif
 
@@ -22,30 +23,30 @@ SYS := $(shell gcc -dumpmachine)
 
 ifneq (, $(findstring linux, $(SYS)))
 # Do linux things
-LDFLAGS		    = -fPIC -lrt -ldl
-OPENSSL_LIBS	?= $(shell pkg-config openssl --libs) 
-OPENSSL_CFLAGS	?= $(shell pkg-config openssl --cflags)
-CFLAGS		    = -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
+LDFLAGS		    += -fPIC -lrt -ldl
+OPENSSL_LIBS	?= $(shell $(PKG_CONFIG) openssl --libs) 
+OPENSSL_CFLAGS	?= $(shell $(PKG_CONFIG) openssl --cflags)
+CFLAGS		    += -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
 endif
 ifneq (, $(findstring apple, $(SYS)))
 # Do darwin things
-LDFLAGS		    = -fPIC -lrt -ldl
-OPENSSL_LIBS	?= $(shell pkg-config openssl --libs) 
-OPENSSL_CFLAGS	?= $(shell pkg-config openssl --cflags)
-CFLAGS		    = -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
+LDFLAGS		    += -fPIC -lrt -ldl
+OPENSSL_LIBS	?= $(shell $(PKG_CONFIG) openssl --libs) 
+OPENSSL_CFLAGS	?= $(shell $(PKG_CONFIG) openssl --cflags)
+CFLAGS		    += -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
 endif
 ifneq (, $(findstring mingw, $(SYS)))
 # Do mingw things
 V			= $(shell lua -e "v=string.gsub('$(LUAV)','%.','');print(v)")
-LDFLAGS		= -mwindows -lcrypt32 -lssl -lcrypto -lws2_32 $(PREFIX)/bin/lua$(V).dll 
+LDFLAGS		+= -mwindows -lcrypt32 -lssl -lcrypto -lws2_32 $(PREFIX)/bin/lua$(V).dll
 LUA_CFLAGS	= -DLUA_LIB -DLUA_BUILD_AS_DLL -I$(PREFIX)/include/
-CFLAGS		= $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
+CFLAGS		+= $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
 endif
 ifneq (, $(findstring cygwin, $(SYS)))
 # Do cygwin things
-OPENSSL_LIBS	?= $(shell pkg-config openssl --libs) 
-OPENSSL_CFLAGS  ?= $(shell pkg-config openssl --cflags)
-CFLAGS		= -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
+OPENSSL_LIBS	?= $(shell $(PKG_CONFIG) openssl --libs) 
+OPENSSL_CFLAGS  ?= $(shell $(PKG_CONFIG) openssl --cflags)
+CFLAGS		+= -fPIC $(OPENSSL_CFLAGS) $(LUA_CFLAGS)
 endif
 #custome config
 ifeq (.config, $(wildcard .config))
@@ -61,7 +62,7 @@ WARN_MOST	= -Wall -W -Waggregate-return -Wcast-align -Wmissing-prototypes -Wnest
 WARN		= -Wall -Wno-unused-value
 WARN_MIN	= 
 CFLAGS		+= $(WARN_MIN) -DPTHREADS 
-CC= gcc -g $(CFLAGS) -Ideps
+CC			?= gcc -g $(CFLAGS) -Ideps
 
 
 OBJS=src/asn1.o src/auxiliar.o src/bio.o src/cipher.o src/cms.o src/compat.o src/crl.o src/csr.o src/dh.o src/digest.o src/dsa.o \