Revision 1887485

Merge r1887279 from trunk:

build/apr_common.m4: avoid explicit inclusion of "confdefs.h"

The failure is observed on `autoconf-2.69d` (soon to be released
as `autoconf-2.70`). There `int64_t` detection fails as:

$ autoreconf && ./configure
checking whether int64_t and int use fmt %d... no
checking whether int64_t and long use fmt %ld... no
checking whether int64_t and long long use fmt %lld... no
configure: error: could not determine the string function for int64_t
```

This happens because `./configure` always stumbles on warning:

configure:3350: gcc -c -g -O2 -Werror  conftest.c >&5
In file included from conftest.c:31:
confdefs.h:22: error: "__STDC_WANT_IEC_60559_ATTRIBS_EXT__" redefined [-Werror]
   22 | #define __STDC_WANT_IEC_60559_ATTRIBS_EXT__ 1
      |

It's triggered by double inclusion of `"confdefs.h"` contents:
explicitly in `APR_TRY_COMPILE_NO_WARNING` macro and implicitly
via `AC_LANG_SOURCE` use.

To fix it and avoid having to define `main()` declaration the change
uses `AC_LANG_PROGRAM` instead.

Tested on both `autoconf-2.69` and `autoconf-2.69d`.


Github: closes #25
Submitted by: Sergei Trofimovich <slyfox gentoo.org>
Reviewed by: ylavic