Fix meson build without zlib

Trying to build with meson with -Dzlib=disabled failed with the
following error message:

cairo/test/meson.build:599:2: ERROR: Unknown variable
"libcairoscript_dep".

This commit fixes that problem by adding a not-found dependency if
cairo-script is not built.

Additionally, follow-up problems are fixed:

- any2ppm.c still tried to include cairo-script-interpreter.h, which was
  not found
- Building cairo-test-trace was attempted, but that also failed because
  of missing script support.

Fixes: https://gitlab.freedesktop.org/cairo/cairo/-/issues/475
Signed-off-by: Uli Schlachter <psychon@znc.in>

test/any2ppm.c

@@ -60,7 +60,10 @@
 #include <string.h>
 
 #include <cairo.h>
+
+#if CAIRO_HAS_INTERPRETER
 #include <cairo-script-interpreter.h>
+#endif
 
 #if CAIRO_CAN_TEST_PDF_SURFACE
 #include <poppler.h>

test/meson.build

@@ -602,7 +602,7 @@ if build_any2ppm
   test_depends += [any2ppm_exe]
 endif
 
-if have_shm
+if have_shm and conf.get('CAIRO_HAS_INTERPRETER', 0) == 1
   cairo_test_trace_exe = executable('cairo-test-trace', cairo_test_trace_sources,
   include_directories: [incbase],
   c_args: pthread_c_args,

util/meson.build

@@ -8,6 +8,8 @@ endif
 
 if conf.get('CAIRO_HAS_INTERPRETER', 0) == 1
   subdir('cairo-script')
+else
+  libcairoscript_dep = dependency('', required: false)
 endif
 
 if conf.get('CAIRO_HAS_TRACE', 0) == 1