ci: Enable PCH in mingw cross job

This will make this job run a bit faster.

Co-authored-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/e52e2c29-4834-4c64-a200-eddcba38fb4d%40eisentraut.org

.github/workflows/pg-ci.yml

@@ -1166,6 +1166,8 @@ jobs:
       # Use larger ccache cache as this job compiles with multiple
       # compilers / flag combinations.
       CCACHE_MAXSIZE: "1G"
+      CCACHE_SLOPPINESS: pch_defines,time_macros
+      CCACHE_DEPEND: 1
 
       # Enable everything else in LINUX_CONFIGURE_FEATURES but not in
       # MESON_COMMON_FEATURES.
@@ -1235,6 +1237,7 @@ jobs:
         env:
           CONF: >-
             --cross-file src/tools/ci/mingw-cross-file.txt
+            -Db_pch=true
             -Dcassert=true
             -Dauto_features=disabled
             -Dzlib=enabled