In this way, the include path with look first for headers in the sr_unix_nsb directory, as instructed in the CMakeLists.txt file.
These source tree was directly imported from http://sourceforge.net/projects/fis-gtm/files/GT.M-x86-Linux-src/V5.4-002B/ by extracting the file: gtm_V54002B_linux_i686_src.tar.gz