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/libstore/build-utils-meson

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

src/libstore/meson.build

@@ -15,7 +15,7 @@ project('nix-store', 'cpp',
 
 cxx = meson.get_compiler('cpp')
 
-subdir('build-utils-meson/deps-lists')
+subdir('nix-meson-build-support/deps-lists')
 
 configdata = configuration_data()
 
@@ -29,7 +29,7 @@ deps_private_maybe_subproject = [
 deps_public_maybe_subproject = [
   dependency('nix-util'),
 ]
-subdir('build-utils-meson/subprojects')
+subdir('nix-meson-build-support/subprojects')
 
 run_command('ln', '-s',
   meson.project_build_root() / '__nothing_link_target',
@@ -81,7 +81,7 @@ if host_machine.system() == 'windows'
   deps_other += [wsock32]
 endif
 
-subdir('build-utils-meson/libatomic')
+subdir('nix-meson-build-support/libatomic')
 
 boost = dependency(
   'boost',
@@ -131,7 +131,7 @@ if aws_s3.found()
 endif
 deps_other += aws_s3
 
-subdir('build-utils-meson/generate-header')
+subdir('nix-meson-build-support/generate-header')
 
 generated_headers = []
 foreach header : [
@@ -179,7 +179,7 @@ add_project_arguments(
   language : 'cpp',
 )
 
-subdir('build-utils-meson/common')
+subdir('nix-meson-build-support/common')
 
 sources = files(
   'binary-cache-store.cc',
@@ -416,8 +416,8 @@ foreach name, value : cpp_str_defines
   ]
 endforeach
 
-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(
   'nixstore',
@@ -446,4 +446,4 @@ if host_machine.system() != 'darwin'
   }
 endif
 
-subdir('build-utils-meson/export')
+subdir('nix-meson-build-support/export')

src/libstore/nix-meson-build-support

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

src/libstore/package.nix

@@ -32,8 +32,8 @@ mkMesonLibrary (finalAttrs: {
 
   workDir = ./.;
   fileset = fileset.unions [
-    ../../build-utils-meson
-    ./build-utils-meson
+    ../../nix-meson-build-support
+    ./nix-meson-build-support
     ../../.version
     ./.version
     ./meson.build