meson: ci: ensure tests are built before running them

Meson 1.7 stopped building all the dependencies of tests as part of the
default build target. But it does breaks CI because we only built the default
target before running the test, and ran the tests with --no-rebuild.

The simplest fix would be to remove --no-rebuild from MTEST_ARGS, but it seems
better to explicitly build the test dependencies, so compiler warnings /
errors are visible as part of the build step.

Discussion: https://postgr.es/m/CAGECzQSvM3iSDmjF+=Kof5an6jN8UbkP_4cKKT9w6GZavmb5yQ@mail.gmail.com
Backpatch: 16-, where meson was added

.cirrus.tasks.yml

@@ -17,6 +17,9 @@ env:
   CHECK: check-world PROVE_FLAGS=$PROVE_FLAGS
   CHECKFLAGS: -Otarget
   PROVE_FLAGS: --timer
+  # Build test dependencies as part of the build step, to see compiler
+  # errors/warnings in one place.
+  MBUILD_TARGET: all testprep
   MTEST_ARGS: --print-errorlogs --no-rebuild -C build
   PGCTLTIMEOUT: 120 # avoids spurious failures during parallel tests
   TEMP_CONFIG: ${CIRRUS_WORKING_DIR}/src/tools/ci/pg_ci_base.conf
@@ -99,7 +102,7 @@ task:
     EOF
   build_script: |
     su postgres <<-EOF
-      ninja -C build -j${BUILD_JOBS}
+      ninja -C build -j${BUILD_JOBS} ${MBUILD_TARGET}
     EOF
   upload_caches: ccache
 
@@ -176,7 +179,7 @@ task:
         -Dextra_lib_dirs=/usr/local/lib -Dextra_include_dirs=/usr/local/include/ \
         build
     EOF
-  build_script: su postgres -c 'ninja -C build -j${BUILD_JOBS}'
+  build_script: su postgres -c 'ninja -C build -j${BUILD_JOBS} ${MBUILD_TARGET}'
   upload_caches: ccache
 
   test_world_script: |
@@ -378,8 +381,8 @@ task:
             build-32
         EOF
 
-      build_script: su postgres -c 'ninja -C build -j${BUILD_JOBS}'
+      build_script: su postgres -c 'ninja -C build -j${BUILD_JOBS} ${MBUILD_TARGET}'
-      build_32_script: su postgres -c 'ninja -C build-32 -j${BUILD_JOBS}'
+      build_32_script: su postgres -c 'ninja -C build-32 -j${BUILD_JOBS} ${MBUILD_TARGET}'
 
       upload_caches: ccache
 
@@ -498,7 +501,7 @@ task:
       -DPG_TEST_EXTRA="$PG_TEST_EXTRA" \
       build
 
-  build_script: ninja -C build -j${BUILD_JOBS}
+  build_script: ninja -C build -j${BUILD_JOBS} ${MBUILD_TARGET}
   upload_caches: ccache
 
   test_world_script: |
@@ -571,7 +574,7 @@ task:
 
   build_script: |
     vcvarsall x64
-    ninja -C build
+    ninja -C build %MBUILD_TARGET%
 
   check_world_script: |
     vcvarsall x64
@@ -629,7 +632,7 @@ task:
     %BASH% -c "meson setup -Ddebug=true -Doptimization=g -Dcassert=true -Db_pch=true -Dnls=disabled -DTAR=%TAR% build"
 
   build_script: |
-    %BASH% -c "ninja -C build"
+    %BASH% -c "ninja -C build ${MBUILD_TARGET}"
 
   upload_caches: ccache