add -pthread and allow make install

GNUmakefile

@@ -6,13 +6,20 @@ CXXFLAGS = -g
 # after turning on -O2. The GCC optimizer may have bugs that cause it to generate incorrect code.
 # Try removing -fdata-sections if you get "undefined external reference" errors.
 # CXXFLAGS = -O2 -DNDEBUG -ffunction-sections -fdata-sections
-# LDFLAGS = -Wl,--gc-sections
+# LDFLAGS += -Wl,--gc-sections
 ARFLAGS = -cr	# ar needs the dash on OpenBSD
 RANLIB = ranlib
+CP = cp
+MKDIR = mkdir
 UNAME = $(shell uname)
 ISX86 = $(shell uname -m | grep -c "i.86\|x86_64")
 ISMINGW = $(shell uname | grep -c "MINGW32")
 
+# Default prefix for make install
+ifeq ($(PREFIX),)
+PREFIX = /usr
+endif
+
 ifeq ($(CXX),gcc)	# for some reason CXX is gcc on cygwin 1.1.4
 CXX = g++
 endif
@@ -42,6 +49,10 @@ else
 CXXFLAGS += -pipe
 endif
 
+ifeq ($(UNAME),Linux)
+LDFLAGS += -pthread
+endif
+
 ifeq ($(UNAME),Darwin)
 AR = libtool
 ARFLAGS = -static -o
@@ -80,6 +91,12 @@ all: cryptest.exe
 clean:
 	$(RM) cryptest.exe libcryptopp.a $(LIBOBJS) $(TESTOBJS) cryptopp.dll libcryptopp.dll.a libcryptopp.import.a cryptest.import.exe dlltest.exe $(DLLOBJS) $(LIBIMPORTOBJS) $(TESTIMPORTOBJS) $(DLLTESTOBJS)
 
+install:
+	$(MKDIR) -p $(PREFIX)/include/cryptopp $(PREFIX)/lib $(PREFIX)/bin
+	$(CP) *.h $(PREFIX)/include/cryptopp
+	$(CP) *.a $(PREFIX)/lib
+	$(CP) *.exe $(PREFIX)/bin
+
 libcryptopp.a: $(LIBOBJS)
 	$(AR) $(ARFLAGS) $@ $(LIBOBJS)
 	$(RANLIB) $@