meson: Use find_program() to resolve the entitlement.sh script

Using ../configure without any particular option generates 31 targets
on Darwin, and meson search for the entitlement.sh script 31 times:

  Program nm found: YES
  Program scripts/undefsym.py found: YES (/opt/homebrew/opt/python@3.9/bin/python3.9 /Code/qemu/scripts/undefsym.py)
  Program scripts/feature_to_c.sh found: YES (/bin/sh /Code/qemu/scripts/feature_to_c.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Program scripts/entitlement.sh found: YES (/Code/qemu/scripts/entitlement.sh)
  Configuring 50-edk2-i386-secure.json using configuration
  Configuring 50-edk2-x86_64-secure.json using configuration

Use find_program() which seems to cache the script path once found.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220122002052.83745-1-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -3052,17 +3052,14 @@ foreach target : target_dirs
         install_input += meson.current_source_dir() / entitlements
       endif
 
+      entitlement = find_program('scripts/entitlement.sh')
       emulators += {exe['name'] : custom_target(exe['name'],
                    input: build_input,
                    output: exe['name'],
-                   command: [
-                     files('scripts/entitlement.sh'),
-                     '@OUTPUT@',
-                     '@INPUT@'
-                   ])
+                   command: [entitlement, '@OUTPUT@', '@INPUT@'])
       }
 
-      meson.add_install_script('scripts/entitlement.sh', '--install',
+      meson.add_install_script(entitlement, '--install',
                                get_option('bindir') / exe['name'],
                                install_input)
     else