[meson] Require 0.55.0

We implicitly require it for building ragel subproject. This new version
requirement should satisfied in both Fedora 33 and Debian bullseye, and
not be too cutting edge for us.
diff --git a/perf/meson.build b/perf/meson.build
index c3b0e3e..e12744c 100644
--- a/perf/meson.build
+++ b/perf/meson.build
@@ -6,12 +6,6 @@
   ttf_parser_dep = subproject('ttf-parser').get_variable('ttf_parser_dep')
 endif
 
-if ttf_parser_dep.found()
-  benchmark_cpp_args = ['-DHAVE_TTFPARSER']
-else
-  benchmark_cpp_args = []
-endif
-
 benchmark('perf', executable('perf', 'perf.cc',
   dependencies: [
     google_benchmark_dep, freetype_dep,
@@ -20,8 +14,8 @@
     # https://github.com/RazrFalcon/ttf-parser/issues/29
     ttf_parser_dep, thread_dep, cpp.find_library('dl'),
   ],
-  cpp_args: benchmark_cpp_args,
+  cpp_args: ttf_parser_dep.found() ? ['-DHAVE_TTFPARSER'] : [],
   include_directories: [incconfig, incsrc],
   link_with: [libharfbuzz],
   install: false,
-), workdir: join_paths(meson.current_source_dir(), '..'), timeout: 100)
+), workdir: meson.current_source_dir() / '..', timeout: 100)