pgsql: Remove long-dead support for platforms without sig_atomic_t.

Remove long-dead support for platforms without sig_atomic_t.

C89 requires <signal.h> to define sig_atomic_t, and there is no evidence
in the buildfarm that any supported platforms don't comply. Remove the
configure test to stop wasting build cycles on a purely historical issue.
(Once upon a time, we cared about supporting C89-compliant compilers on
machines with pre-C89 system headers, but that use-case has been dead for
quite a few years.)

I have some other fixes planned in this area, but let's start with this
to see if the buildfarm produces any surprising results.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/0f19d0f12fa235c6951ff431bd60da594356a1a6

Modified Files
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configure | 14 --------------
configure.in | 4 ----
src/include/c.h | 5 -----
src/include/pg_config.h.in | 3 ---
src/include/pg_config.h.win32 | 3 ---
5 files changed, 29 deletions(-)