Reintroduce project-scoped Zig global cache.

7489516 reverted the workaround we had in place
for random Zig failures when building in parallel. While we don't want a global
cache for every inner build, we *do* want a global cache for the project as a
whole in order to isolate the build from the rest of the machine as much as we
can.

Author: alexrp

src/sdk/build/Vezel.Zig.Sdk.Build.targets

@@ -63,7 +63,7 @@
                     DocumentationAnalysis="$(DocumentationAnalysis)"
                     DynamicImageBase="$(DynamicImageBase)"
                     EagerBinding="$(EagerBinding)"
-                    EnvironmentVariables="ZIG_LOCAL_CACHE_DIR=$(CachePath)"
+                    EnvironmentVariables="ZIG_GLOBAL_CACHE_DIR=$(GlobalCachePath); ZIG_LOCAL_CACHE_DIR=$(LocalCachePath)"
                     FastMath="$(FastMath)"
                     ImageBase="$(ImageBase)"
                     IncludeDirectories="@(IncludeDirectory)"

src/sdk/build/Vezel.Zig.Sdk.Clean.targets

@@ -1,8 +1,9 @@
 <!-- SPDX-License-Identifier: 0BSD -->
 
 <Project>
-    <ItemGroup>
-        <Clean Include="$(CachePath)/**" />
+    <ItemGroup Condition="'$(IsOuterBuild)' != 'true'">
+        <Clean Include="$(GlobalCachePath)/**" />
+        <Clean Include="$(LocalCachePath)/**" />
         <Clean Include="$(_CommandFragmentsPath)/**" />
     </ItemGroup>
 

src/sdk/build/Vezel.Zig.Sdk.Defaults.targets

@@ -7,7 +7,8 @@
     -->
 
     <PropertyGroup>
-        <CachePath Condition="'$(CachePath)' == ''">$(IntermediateOutputPath)zig-cache</CachePath>
+        <GlobalCachePath Condition="'$(CachePath)' == ''">$(BaseIntermediateOutputPath)zig-cache</GlobalCachePath>
+        <LocalCachePath Condition="'$(CachePath)' == ''">$(IntermediateOutputPath)zig-cache</LocalCachePath>
         <CommandsPath Condition="'$(CommandsPath)' == ''">$(IntermediateOutputPath)compile_commands.json</CommandsPath>
         <DefaultSources Condition="'$(DefaultSources)' == ''">true</DefaultSources>
         <EditorSupport Condition="'$(EditorSupport)' == ''">true</EditorSupport>

src/sdk/build/Vezel.Zig.Sdk.Editor.targets

@@ -37,11 +37,11 @@
         <!--
         The Zig compiler will not emit a new compilation database fragment for a
         given source file if it has not actually changed. This unfortunately
-        means that we have to clean the entire Zig cache when we need to refresh
-        compile_commands.json. Fun.
+        means that we have to clean the entire local Zig cache when we need to
+        refresh compile_commands.json. Fun.
         -->
-        <RemoveDir Directories="$(CachePath)"
-                   Condition="Exists('$(CachePath)')" />
+        <RemoveDir Directories="$(LocalCachePath)"
+                   Condition="Exists('$(LocalCachePath)')" />
     </Target>
 
     <!--

src/sdk/build/Vezel.Zig.Sdk.Test.targets

@@ -35,7 +35,7 @@
                     DocumentationAnalysis="$(DocumentationAnalysis)"
                     DynamicImageBase="$(DynamicImageBase)"
                     EagerBinding="$(EagerBinding)"
-                    EnvironmentVariables="ZIG_LOCAL_CACHE_DIR=$(CachePath)"
+                    EnvironmentVariables="ZIG_GLOBAL_CACHE_DIR=$(GlobalCachePath); ZIG_LOCAL_CACHE_DIR=$(LocalCachePath)"
                     FastMath="$(FastMath)"
                     ImageBase="$(ImageBase)"
                     IncludeDirectories="@(IncludeDirectory)"