newlib: avoid duplicate awk checks

newlib: avoid duplicate awk checks

Since AM_INIT_AUTOMAKE calls AC_PROG_AWK, and some configure.ac
scripts call it too, we end up testing for awk multiple times.  If
we change NEWLIB_CONFIGURE to require the macro instead, then it
makes sure it's always expanded, but only once.

While we're here, do the same thing with AC_PROG_INSTALL since it
is also called by AM_INIT_AUTOMAKE, although it doesn't currently
result in duplicate configure checks.