build.plat: allow spaces in environment variables on Windows.

Specifically, allow spaces in:
- set AMARANTH_ENV_<toolchain>=c:\program files\...
- set <tool>=c:\program files\...

Author: whitequark

amaranth/build/plat.py

@@ -184,7 +184,8 @@ class TemplatedPlatform(Platform):
         "build_{{name}}.bat": """
             @rem {{autogenerated}}
             {{quiet("@echo off")}}
-            if defined {{platform._toolchain_env_var}} call %{{platform._toolchain_env_var}}%
+            SetLocal EnableDelayedExpansion
+            if defined {{platform._toolchain_env_var}} call "%{{platform._toolchain_env_var}}%"
             {{emit_commands("bat")}}
         """,
     }
@@ -283,8 +284,8 @@ def emit_commands(syntax):
                     template = ": ${{{env_var}:={name}}}"
                 elif syntax == "bat":
                     template = \
-                        "if [%{env_var}%] equ [\"\"] set {env_var}=\n" \
-                        "if [%{env_var}%] equ [] set {env_var}={name}"
+                        "if [!{env_var}!] equ [\"\"] set {env_var}=\n" \
+                        "if [!{env_var}!] equ [] set {env_var}={name}"
                 else:
                     assert False
                 commands.append(template.format(env_var=env_var, name=name))
@@ -308,7 +309,7 @@ def invoke_tool(context, name):
             if context.parent["syntax"] == "sh":
                 return f"\"${env_var}\""
             elif context.parent["syntax"] == "bat":
-                return f"%{env_var}%"
+                return f"\"%{env_var}%\""
             else:
                 assert False