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-test-support/build-utils-meson

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

src/libexpr-test-support/meson.build

@@ -14,7 +14,7 @@ project('nix-expr-test-support', 'cpp',
 
 cxx = meson.get_compiler('cpp')
 
-subdir('build-utils-meson/deps-lists')
+subdir('nix-meson-build-support/deps-lists')
 
 deps_private_maybe_subproject = [
 ]
@@ -26,7 +26,7 @@ deps_public_maybe_subproject = [
   dependency('nix-expr'),
   dependency('nix-expr-c'),
 ]
-subdir('build-utils-meson/subprojects')
+subdir('nix-meson-build-support/subprojects')
 
 rapidcheck = dependency('rapidcheck')
 deps_public += rapidcheck
@@ -40,7 +40,7 @@ add_project_arguments(
   language : 'cpp',
 )
 
-subdir('build-utils-meson/common')
+subdir('nix-meson-build-support/common')
 
 sources = files(
   'tests/value/context.cc',
@@ -54,8 +54,8 @@ headers = files(
   'tests/value/context.hh',
 )
 
-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(
   'nix-expr-test-support',
@@ -73,4 +73,4 @@ install_headers(headers, subdir : 'nix', preserve_path : true)
 
 libraries_private = []
 
-subdir('build-utils-meson/export')
+subdir('nix-meson-build-support/export')

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

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

src/libexpr-test-support/package.nix

@@ -23,8 +23,8 @@ mkMesonLibrary (finalAttrs: {
 
   workDir = ./.;
   fileset = fileset.unions [
-    ../../build-utils-meson
-    ./build-utils-meson
+    ../../nix-meson-build-support
+    ./nix-meson-build-support
     ../../.version
     ./.version
     ./meson.build