Log Message:
Don't require c99 in USE_LANGUAGES. libiconv builds fine with gcc
2.95.4 on FreeBSD 4.11 without it; with it, pkgsrc wants gcc3-c,
which results in a circular dependency.

The addition of c99 to USE_LANGUAGES appears to have been intended
to benefit IRIX with MIPSPro, so also restore the old behavior of
appending "-c99" to CFLAGS in that case.