gsl-1.2: build problem on IBM AIX 4.2, and a simple workaround

[Brian Gough]

Nelson H. F. Beebe writes:
 > The build of gsl-1.2 with gcc-2.95.3 on IBM RS/6000 AIX 4.2 failed
 > like this:
 > 	ld: 0711-781 ERROR: TOC overflow. TOC size: 72184 Maximum
 > size: 65536
 > 	collect2: ld returned 12 exit status
 > I restarted it with
 > 	make LDFLAGS=-Wl,-bigtoc
 > and the make then succeeded, as did the validation tests and
 > installation.

Thanks. Should now be noted in the INSTALL file.