meson: do not set global cxxflags

this is so that libostd can work as a subproject

examples/meson.build

@@ -20,6 +20,7 @@ foreach example: libostd_examples_src
         [example],
         dependencies: [libostd, thread_dep],
         include_directories: libostd_includes,
+        cpp_args: extra_cxxflags,
         install: false
     )
 endforeach

meson.build

@@ -16,12 +16,10 @@ unicode_data = join_paths('data', 'UnicodeData-11.0.txt')
 libostd_includes = [include_directories('.')]
 
 tgt_compiler_id = meson.get_compiler('cpp').get_id()
-
 if tgt_compiler_id == 'gcc' or tgt_compiler_id == 'clang'
-    add_global_arguments(
-        '-Wextra', '-Wshadow', '-Wold-style-cast',
-        language: 'cpp'
-    )
+    extra_cxxflags = ['-Wextra', '-Wshadow', '-Wold-style-cast']
+else
+    extra_cxxflags = []
 endif
 
 subdir('src')

src/meson.build

@@ -49,7 +49,7 @@ thread_dep = dependency('threads')
 libostd_gen_unicode_exe = executable('gen_unicode',
     ['../gen_unicode.cc'],
     include_directories: libostd_includes,
-    cpp_args: '-DOSTD_GEN_UNICODE_BUILD',
+    cpp_args: extra_cxxflags + ['-DOSTD_GEN_UNICODE_BUILD'],
     install: false,
     native: true
 )
@@ -70,6 +70,7 @@ libostd_lib = library('ostd',
     libostd_src, libostd_extra_src,
     dependencies: thread_dep,
     include_directories: libostd_includes + [include_directories('.')],
+    cpp_args: extra_cxxflags,
     install: true,
     version: meson.project_version()
 )

tests/meson.build

@@ -2,6 +2,7 @@ test_runner_exe = executable('test_runner',
     ['test_runner.cc'],
     dependencies: libostd,
     include_directories: libostd_includes,
+    cpp_args: extra_cxxflags,
     install: false
 )
 
@@ -16,6 +17,7 @@ foreach test_src: libostd_tests_src
         [test_src],
         dependencies: libostd,
         include_directories: libostd_includes,
+        cpp_args: extra_cxxflags,
         install: false
     )
 endforeach