[patch #6848] ac_c_printf_thsep.m4: Does ac_try_compile suffice?

[Peter Simons]

Update of patch #6848 (project autoconf-archive):

                  Status:             In Progress => Done                   
             Open/Closed:                    Open => Closed                 

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Follow-up Comment #3:

The macro in its current form has been marked obsolete, because it cannot
reliably detect whether %' is supported or not. The fact that false positive
results may occur is particularly unpleasant. In order to be reliable, the
macro would have to test a cascade of properties:

1) Does the compiler fail to translate a broken %s or %d format string?

2) Does the compiler fail to translate a broken %' format string?

3) Does the compiler translate a proper %' format string?

4) When run, does sprinf() generate the expected result for %'?

Now, if running test programs is fine, then testing properties (3) and (4)
suffices to determine a result.

If test programs cannot be run, i.e. because the build takes place in a
cross-compilation environment, then properties (1), (2), and (3) can be tested
to determine a result that is not quite perfect -- because the target
platform's libc might still be broken --, but at least we know for certain (no
false-positives) that the *compiler* does recognize %' in format strings.

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