build(header_install_dir): added header_install_dir option

this is useful for wheel builds

build-config/CLI11/meson.build

@@ -4,5 +4,5 @@ cli11_dep = cli11_proj.get_variable('CLI11_dep')
 cli11_headers = cli11_proj.get_variable('cli11_headers')
 cli11_impl_headers = cli11_proj.get_variable('cli11_impl_headers')
 
-install_headers(cli11_headers, subdir: 'fourdst/vendor/CLI')
-install_headers(cli11_impl_headers, subdir: 'fourdst/vendor/CLI/impl')
+install_headers(cli11_headers,      install_dir: config_header_root / 'fourdst' / 'vendor' / 'CLI')
+install_headers(cli11_impl_headers, install_dir: config_header_root / 'fourdst' / 'vendor' / 'CLI' / 'impl')

build-config/reflect-cpp/meson.build

@@ -33,6 +33,6 @@ reflect_cpp_dep = declare_dependency(
 
 install_subdir(
     'include',
-    install_dir: get_option('includedir') / 'fourdst' / 'vendor',
-    strip_directory: true
+    install_dir: config_header_root / 'fourdst' / 'vendor',
+    strip_directory: true,
 )

build-config/tomlpp/meson.build

@@ -2,8 +2,7 @@ tomlpp_inc_dir = include_directories('vendor/include')
 
 install_subdir(
     'vendor/include',
-    install_dir: get_option('includedir') / 'fourdst' / 'vendor',
-    strip_directory: true
+    install_dir: config_header_root / 'fourdst' / 'vendor',
+    strip_directory: true,
+    exclude_files: ['meson.build'],
 )
-
-