Switch to "meson setup"

Fixes this warning:

    WARNING: Running the setup command as `meson [options]` instead of `meson setup [options]` is ambiguous and deprecated.

.builds/alpine.yml

@@ -24,7 +24,7 @@ sources:
 tasks:
   - setup: |
       cd wlroots
-      meson build --fatal-meson-warnings --default-library=both -Dauto_features=enabled -Dxcb-errors=disabled
+      meson setup build --fatal-meson-warnings --default-library=both -Dauto_features=enabled -Dxcb-errors=disabled
   - build: |
       cd wlroots
       ninja -C build

.builds/archlinux.yml

@@ -25,8 +25,8 @@ sources:
 tasks:
   - setup: |
       cd wlroots
-      CC=gcc meson build-gcc --fatal-meson-warnings --default-library=both -Dauto_features=enabled --prefix /usr -Db_sanitize=address,undefined
-      CC=clang meson build-clang --fatal-meson-warnings -Dauto_features=enabled
+      CC=gcc meson setup build-gcc --fatal-meson-warnings --default-library=both -Dauto_features=enabled --prefix /usr -Db_sanitize=address,undefined
+      CC=clang meson setup build-clang --fatal-meson-warnings -Dauto_features=enabled
   - gcc: |
       cd wlroots/build-gcc
       ninja

.builds/freebsd.yml

@@ -32,7 +32,7 @@ sources:
 tasks:
   - wlroots: |
       cd wlroots
-      meson build --fatal-meson-warnings -Dauto_features=enabled
+      meson setup build --fatal-meson-warnings -Dauto_features=enabled
       ninja -C build
       sudo ninja -C build install
   - tinywl: |

README.md

@@ -64,7 +64,7 @@ If you choose to enable X11 support:
 
 Run these commands:
 
-    meson build/
+    meson setup build/
     ninja -C build/
 
 Install like so: