Remove unncessary use of PWD in CPP include option.

The use of an absolute path can sometimes leads to compile errors using
Jenkins on Windows. The form without PWD seems to build correctly on
several varieties of each of Linux, OS X, and Windows.

Makefile

@@ -41,7 +41,7 @@ arch_flags : arch_flags.c
 ARCHFLAGS ?= $(shell $(CC) arch_flags.c -o arch_flags && ./arch_flags)
 OPTFLAGS  ?= -g -O #-DABC_NAMESPACE=xxx
 
-CFLAGS   += -Wall -Wno-unused-function -Wno-write-strings -Wno-sign-compare $(OPTFLAGS) $(ARCHFLAGS) -I$(PWD)/src
+CFLAGS   += -Wall -Wno-unused-function -Wno-write-strings -Wno-sign-compare $(OPTFLAGS) $(ARCHFLAGS) -Isrc
 
 # Set -Wno-unused-bug-set-variable for GCC 4.6.0 and greater only
 ifneq ($(or $(findstring gcc,$(CC)),$(findstring g++,$(CC))),)