meson: Run ECPG tests in runnable cross builds

The ECPG tests need to run the host ecpg binary to generate test
dependencies.  They are currently disabled for every cross build, even
when the build machine can run host binaries directly or through an
executable wrapper.

Use meson.can_run_host_binaries() to skip the tests only when host
binaries cannot run.  The preceding patch makes the regression test
harness honor an executable wrapper.

Author: Harrison-Booth

src/interfaces/ecpg/test/meson.build

@@ -1,7 +1,7 @@
 # Copyright (c) 2022-2026, PostgreSQL Global Development Group
 
-# can't run ecpg to build test dependencies, at least not without an emulator
-if meson.is_cross_build()
+# We need to run ecpg to build test dependencies.
+if not meson.can_run_host_binaries()
   subdir_done()
 endif