Default to ninja for faster builds

Require ninja by default for a predictable build experience on Unix
platforms. Users can opt out with --ninja false.

Contributes to #54022

Author: steveisok

eng/build.sh

@@ -84,7 +84,7 @@ usage()
   echo "  --gccx.y                   Optional argument to build using gcc version x.y."
   echo "  --portablebuild            Optional argument: set to false to force a non-portable build."
   echo "  --keepnativesymbols        Optional argument: set to true to keep native symbols/debuginfo in generated binaries."
-  echo "  --ninja                    Optional argument: use Ninja instead of Make (default: true if ninja is installed, use --ninja false to disable)."
+  echo "  --ninja                    Optional argument: use Ninja instead of Make (default: true, use --ninja false to disable)."
   echo "  --pgoinstrument            Optional argument: build PGO-instrumented runtime"
   echo "  --fsanitize                Optional argument: Specify native sanitizers to instrument the native build with. Supported values are: 'address'."
   echo ""
@@ -166,12 +166,8 @@ source $scriptroot/common/native/init-os-and-arch.sh
 
 hostArch=$arch
 
-# Default to using Ninja if installed for faster builds (can be overridden with --ninja false)
-if command -v ninja &> /dev/null; then
-  useNinja=true
-else
-  useNinja=false
-fi
+# Default to using Ninja for faster builds (can be overridden with --ninja false)
+useNinja=true
 
 # Check if an action is passed in
 declare -a actions=("b" "build" "r" "restore" "rebuild" "testnobuild" "sign" "publish" "clean")

eng/native/build-commons.sh

@@ -271,7 +271,7 @@ usage()
     echo "        will use ROOTFS_DIR environment variable if set."
     echo "-gcc: optional argument to build using gcc in PATH."
     echo "-gccx.y: optional argument to build using gcc version x.y."
-    echo "-ninja: target ninja instead of GNU make (default on macOS, use -ninja false to disable)"
+    echo "-ninja: target ninja instead of GNU make (default: true, use -ninja false to disable)"
     echo "-numproc: set the number of build processes."
     echo "-targetrid: optional argument that overrides the target rid name."
     echo "-portablebuild: pass -portablebuild=false to force a non-portable build."
@@ -311,11 +311,8 @@ else
   __NumProc=1
 fi
 
-# Default to using Ninja on macOS for faster builds
-__UseNinja=0
-if [[ "$os" == "osx" ]]; then
-  __UseNinja=1
-fi
+# Default to using Ninja for faster builds
+__UseNinja=1
 
 while :; do
     if [[ "$#" -le 0 ]]; then