pgsql: Provide error hint on exit() check when building libpq

Provide error hint on exit() check when building libpq

Commit dc227eb82 introduced a restriction on libpq that no functions which
invoke exit() are allowed to be called. This was further refined and fixed
in e45b0dfa1f and 2f7bae2f92 and 792259591. While this is well documented
in the Makefile, the error message emitted when the check failed was terse,
without hints for new developers without prior context. This adds an error
hint to assist new developers onboarding to postgres.

Author: Rachel Heaton <rheaton(at)vmware(dot)com>
Co-authored-by: Jacob Champion <pchampion(at)vmware(dot)com>
Discussion: https://postgr.es/m/CADJcwiVL20955HCNzDqz9BEDr6A77pz6-nac5sbZVvhAEMijLg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e9bc0441f1446f6614fa6712841acec91890e089

Modified Files
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src/interfaces/libpq/Makefile | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)