pgsql: pkg-config Requires.private entries should be comma-separated

pkg-config Requires.private entries should be comma-separated

In the .pc (pkg-config) files generated by the make and meson builds,
the Requires.private entries use different delimiters. The make build
uses spaces, the meson build uses commas. The pkg-config documentation
says that it should be comma-separated, but apparently about half the
.pc in the wild use just spaces. The pkg-config source code
acknowledges that both commas and spaces work.

This changes the make build to use commas, for consistency.

Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://www.postgresql.org/message-id/flat/1fb52d61-0964-2d8e-87d9-e8be830e2b24%40enterprisedb.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/4ef1be5a0b676a9f030cc2e4837f4b5650ecb069

Modified Files
--------------
src/interfaces/ecpg/compatlib/Makefile | 2 +-
src/interfaces/ecpg/ecpglib/Makefile | 2 +-
src/interfaces/libpq/Makefile | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)