rename: build-utils-meson -> nix-meson-build-support

Fix a footgun. In my case, I had a couple of build ("output")
directories sitting around.

    rm -rf build-*

Was confused for a bit why a meson.build file was missing.

Probably also helps with autocompletion.

I tried meson-build-support first, but I had to add something like
a nix- prefix, in order to make meson happy. They've reserved the
meson- prefix.

src/libexpr-c/build-utils-meson

@@ -1 +0,0 @@
-../../build-utils-meson

src/libexpr-c/meson.build

@@ -14,7 +14,7 @@ project('nix-expr-c', 'cpp',
 
 cxx = meson.get_compiler('cpp')
 
-subdir('build-utils-meson/deps-lists')
+subdir('nix-meson-build-support/deps-lists')
 
 configdata = configuration_data()
 
@@ -27,7 +27,7 @@ deps_public_maybe_subproject = [
   dependency('nix-util-c'),
   dependency('nix-store-c'),
 ]
-subdir('build-utils-meson/subprojects')
+subdir('nix-meson-build-support/subprojects')
 
 # TODO rename, because it will conflict with downstream projects
 configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
@@ -53,7 +53,7 @@ add_project_arguments(
   language : 'cpp',
 )
 
-subdir('build-utils-meson/common')
+subdir('nix-meson-build-support/common')
 
 sources = files(
   'nix_api_expr.cc',
@@ -72,8 +72,8 @@ headers = [config_h] + files(
 # TODO move this header to libexpr, maybe don't use it in tests?
 headers += files('nix_api_expr_internal.h')
 
-subdir('build-utils-meson/export-all-symbols')
-subdir('build-utils-meson/windows-version')
+subdir('nix-meson-build-support/export-all-symbols')
+subdir('nix-meson-build-support/windows-version')
 
 this_library = library(
   'nixexprc',
@@ -89,4 +89,4 @@ install_headers(headers, subdir : 'nix', preserve_path : true)
 
 libraries_private = []
 
-subdir('build-utils-meson/export')
+subdir('nix-meson-build-support/export')

src/libexpr-c/nix-meson-build-support

@@ -0,0 +1 @@
+../../nix-meson-build-support

src/libexpr-c/package.nix

@@ -20,8 +20,8 @@ mkMesonLibrary (finalAttrs: {
 
   workDir = ./.;
   fileset = fileset.unions [
-    ../../build-utils-meson
-    ./build-utils-meson
+    ../../nix-meson-build-support
+    ./nix-meson-build-support
     ../../.version
     ./.version
     ./meson.build