makefile.unix: Removed redundant use of wx-config in DEFS (it was being included twice).

Also changed wx-config --cppflags to --cxxflags. I am not sure what the
    difference is supposed to be, but --cppflags does not include -pthread.

makefile.unix

@@ -4,7 +4,7 @@
 
 CXX=g++
 
-WXINCLUDEPATHS:=$(shell wx-config --cppflags)
+WXINCLUDEPATHS:=$(shell wx-config --cxxflags)
 
 WXLIBS:=$(shell wx-config --libs)
 
@@ -23,7 +23,7 @@ LIBS= \
    -l z \
    -l dl
 
-DEFS:=$(shell wx-config --cxxflags) -DNOPCH -DFOURWAYSSE2 -DUSE_SSL
+DEFS=-DNOPCH -DFOURWAYSSE2 -DUSE_SSL
 DEBUGFLAGS=-g -D__WXDEBUG__
 CXXFLAGS=-O2 -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS) $(WXINCLUDEPATHS)
 HEADERS=headers.h strlcpy.h serialize.h uint256.h util.h key.h bignum.h base58.h \