pgsql: Fix "quiet inline" configure test for newer clang compilers.

Fix "quiet inline" configure test for newer clang compilers.

This test used to just define an unused static inline function and check
whether that causes a warning.  But newer clang versions warn about
unused static inline functions when defined inside a .c file, but not
when defined in an included header, which is the case we care about.
Change the test to cope.

Andres Freund

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/e70980747dbe50b5ddc9aee88912e78825cacdd1

Modified Files
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config/c-compiler.m4        |   15 +++++++++++++--
config/test_quiet_include.h |    5 +++++
configure                   |    2 +-
3 files changed, 19 insertions(+), 3 deletions(-)