Use getcwd() to construct path when WAL path is relative.

Using pg1-path, as we were doing previously, could lead to WAL being copied to/from unexpected places.  PostgreSQL sets the current working directory to PGDATA so we can use that to resolve relative paths.

test/src/module/command/archiveGetTest.c

@@ -623,6 +623,8 @@ testRun(void)
 
         // Write out a WAL segment for success
         // -------------------------------------------------------------------------------------------------------------------------
+        THROW_ON_SYS_ERROR(chdir(strPtr(cfgOptionStr(cfgOptPgPath))) != 0, PathMissingError, "unable to chdir()");
+
         storagePutNP(
             storageNewWriteNP(storageSpoolWrite(), strNewFmt(STORAGE_SPOOL_ARCHIVE_IN "/%s", strPtr(walSegment))),
             BUFSTRDEF("SHOULD-BE-A-REAL-WAL-FILE"));