The intent is to allow compilation with `-Wundef', which in turn should
make it easier to catch erroneous uses of nonexistent macros.
* libguile/__scm.h: Don't assume `BUILDING_LIBGUILE' is defined.
* libguile/conv-uinteger.i.c (SCM_TO_TYPE_PROTO): Remove unneeded CPP
conditional on `TYPE_MIN == 0'.
* libguile/fports.c: Check for the definition of `HAVE_CHSIZE' and
`HAVE_FTRUNCATE', not for their value.
* libguile/ports.c: Likewise.
* libguile/numbers.c (guile_ieee_init): Likewise with `HAVE_DINFINITY'
and `HAVE_DQNAN'.
* test-suite/standalone/test-conversion.c (ieee_init): Likewise.
* libguile/strings.c: Likewise with `SCM_STRING_LENGTH_HISTOGRAM'.
* libguile/strings.h: Likewise.
* libguile/tags.h: Likewise with `HAVE_INTTYPES_H' and `HAVE_STDINT_H'.
* libguile/threads.c: Likewise with `HAVE_PTHREAD_GET_STACKADDR_NP'.
* libguile/vm-engine.c (VM_NAME): Likewise with `VM_CHECK_IP'.
* libguile/gen-scmconfig.c (main): Use "#ifdef HAVE_", not "#if HAVE_".
* libguile/socket.c (scm_setsockopt): Likewise.