Contrary to many people's belief, the C environment on the RS/6000 is
not very special. The C compiler has quite a number of options that can
be used to control how it works, which "dialect" of C it compiles, how
it interprets certain language constructs, etc. InfoExplorer includes a
Users Guide and a Reference Manual.
The compiler can be invoked with either xlc for strict ANSI mode and cc
for RT compatible mode (i.e. IBM 6150 with AIX 2). The default options
for each mode are set in the /etc/xlc.cfg file, and you can actually add
another stanza and create a link to the /bin/xlc executable.
The file /usr/lpp/xlc/bin/README.xlc has information about the C
compiler, and the file /usr/lpp/bos/bsdport (AIX 3 only) contains useful
information, in particular for users from a BSD background.
The file /etc/xlc.cfg also shows the symbol _IBMR2 that is predefined,
and therefore can be used for #ifdef'ing RS/6000 specific code.