pgsql: meson: Tie adding C++ support to the llvm Meson option

meson: Tie adding C++ support to the llvm Meson option

In the event the llvm option is defined to be 'auto', it is possible
that the host machine might not have a C++ compiler. If that is the
case, then we shouldn't continue reaching for the llvm dependency.

To make it easier to understand the case where LLVM support is disabled due to
lacking a C++ compiler, add a message noting that fact.

Author: Tristan Partin <tristan(at)neon(dot)tech>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/CSPIJVUDZFKX.3KHMOAVGF94RV@c3po
Backpatch: 16-, where meson support was added

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7a7f13afee9229fe738c390d39aa44c394400c04

Modified Files
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meson.build | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)