fix(build): wrap toolchain paths in double quotes

Fix issue with Windows paths containing spaces. Recent toolchain
refactoring (cc277de) caused a regression in the Windows build. Ensure
toolchain path utilities wrap paths in double quoted strings.

Change-Id: I7a136e459d85cff1e9851aedf0a5272a841df09c
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Signed-off-by: Chris Kay <chris.kay@arm.com>
Co-authored-by: Chris Kay <chris.kay@arm.com>
diff --git a/make_helpers/unix.mk b/make_helpers/unix.mk
index d285799..93e1fcc 100644
--- a/make_helpers/unix.mk
+++ b/make_helpers/unix.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2024, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -59,5 +59,5 @@
 
     nul := /dev/null
 
-    which = $(shell which $(1) 2>$(nul))
+    which = $(shell command -v $(call escape-shell,$(1)) 2>$(nul))
 endif