target/xtensa: list cores in a text file

Avoid that leftover files affect the build; instead, use the same
mechanism that was in place before the Meson transition of updating
a file from import_core.sh.  Starting with Meson 0.57, the file
can be easily read from the filesystem module, so do that instead
of using run_command.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/xtensa/cores.list

@@ -0,0 +1,9 @@
+core-dc232b.c
+core-dc233c.c
+core-de212.c
+core-de233_fpu.c
+core-dsp3400.c
+core-fsf.c
+core-sample_controller.c
+core-test_kc705_be.c
+core-test_mmuhifi_c3.c

target/xtensa/import_core.sh

@@ -66,3 +66,6 @@ static XtensaConfig $NAME __attribute__((unused)) = {
 
 REGISTER_CORE($NAME)
 EOF
+
+grep -qxf core-${NAME}.c "$BASE"/cores.list || \
+    echo core-${NAME}.c >> "$BASE"/cores.list

target/xtensa/meson.build

@@ -1,7 +1,7 @@
 xtensa_ss = ss.source_set()
 
-xtensa_cores = run_command('sh', '-c', 'cd $MESON_SOURCE_ROOT/$MESON_SUBDIR ; ls -1 core-*.c')
-xtensa_ss.add(files(xtensa_cores.stdout().strip().split('\n')))
+xtensa_cores = fs.read('cores.list')
+xtensa_ss.add(files(xtensa_cores.strip().split('\n')))
 
 xtensa_ss.add(files(
   'cpu.c',