pgsql: Improve compiler string shown in version()

Improve compiler string shown in version()

With some compilers such as Clang and ICC emulating GCC, using a
version string of the form "GCC $version" can be quite misleading.
Also, a great while ago, the version output from gcc --version started
including the string "gcc", so it is redundant to repeat that. In
order to support ancient GCC versions, we now prefix the result with
"GCC " only if the version output does not start with a letter.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8dd2ede3f82505c3fd041c1953524305df0732d1

Modified Files
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configure | 3 ++-
configure.in | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)