Automake includes some support for assembly code. There are two forms
of assembler files: normal (*.s) and preprocessed by CPP
(*.S or *.sx).
The variable CCAS holds the name of the compiler used to build
assembly code. This compiler must work a bit like a C compiler; in
particular it must accept -c and -o. The values of
CCASFLAGS and AM_CCASFLAGS (or its per-target
definition) is passed to the compilation. For preprocessed files,
DEFS, DEFAULT_INCLUDES, INCLUDES, CPPFLAGS
and AM_CPPFLAGS are also used.
The autoconf macro AM_PROG_AS will define CCAS and
CCASFLAGS for you (unless they are already set, it simply sets
CCAS to the C compiler and CCASFLAGS to the C compiler
flags), but you are free to define these variables by other means.
Only the suffixes .s, .S, and .sx are recognized by
automake as being files containing assembly code.