Multiple build runners

[leecannon]

This PR uses a different build runner based on the runtime zig version.

This is not exactly aligned with the decision in #1020 but the maintenance burden to do this is not large:

• On a new major release being tagged make a copy of build_runner/master.zig for that release and update the build_runner/BuildRunnerVersion.zig enum.
• If the data output by the build runner is changed (build_runner/BuildConfig.zig) then the older build runners will need to be updated to match the json format.

Fixes #1396

[Techatrix]

If you want, you can apply this patch to simplify the logic in BuildRunnerVersion.zig
I guess you did this because you didn't want to have the patch version in the enum but adding it in makes it so much simpler.

diff --git a/src/build_runner/0.10.zig b/src/build_runner/0.10.0.zig
similarity index 100%
rename from src/build_runner/0.10.zig
rename to src/build_runner/0.10.0.zig
diff --git a/src/build_runner/0.11.zig b/src/build_runner/0.11.0.zig
similarity index 100%
rename from src/build_runner/0.11.zig
rename to src/build_runner/0.11.0.zig
diff --git a/src/build_runner/BuildRunnerVersion.zig b/src/build_runner/BuildRunnerVersion.zig
index 7a2028a..24ef916 100644
--- a/src/build_runner/BuildRunnerVersion.zig
+++ b/src/build_runner/BuildRunnerVersion.zig
@@ -5,8 +5,8 @@ const build_options = @import("build_options");
 // There should be no need to have a build runner for minor patches (e.g. 0.10.1)
 pub const BuildRunnerVersion = enum {
     master,
-    @"0.11",
-    @"0.10",
+    @"0.11.0",
+    @"0.10.0",
 
     pub fn selectBuildRunnerVersion(runtime_zig_version: std.SemanticVersion) BuildRunnerVersion {
         const runtime_zig_version_simple = std.SemanticVersion{
@@ -23,44 +23,18 @@ pub const BuildRunnerVersion = enum {
         return switch (runtime_zig_version_simple.order(zls_version_simple)) {
             .eq, .gt => .master,
             .lt => blk: {
-                const build_runners = BuildRunnerVersion.non_master_build_runners;
-
-                for (build_runners) |build_runner| {
-                    switch (runtime_zig_version.order(build_runner.version)) {
-                        .eq, .gt => break :blk build_runner.tag,
+                const available_versions = std.meta.tags(BuildRunnerVersion);
+                for (available_versions[1..]) |build_runner_version| {
+                    const version = std.SemanticVersion.parse(@tagName(build_runner_version)) catch unreachable;
+                    switch (runtime_zig_version.order(version)) {
+                        .eq, .gt => break :blk build_runner_version,
                         .lt => {},
                     }
                 }
 
                 // failed to find compatible build runner, falling back to oldest supported version
-                break :blk BuildRunnerVersion.oldest_version;
+                break :blk available_versions[available_versions.len - 1];
             },
         };
     }
-
-    const oldest_version = blk: {
-        const tags = std.meta.tags(BuildRunnerVersion);
-        break :blk tags[tags.len - 1];
-    };
-
-    const NonMasterBuildRunner = struct { tag: BuildRunnerVersion, version: std.SemanticVersion };
-
-    const non_master_build_runners = blk: {
-        const tags = std.meta.tags(BuildRunnerVersion);
-
-        var build_runners: [tags.len - 1]NonMasterBuildRunner = .{};
-
-        var i: usize = 0;
-
-        for (tags) |tag| {
-            if (tag == .master) continue;
-            build_runners[i] = .{
-                .tag = tag,
-                .version = std.SemanticVersion.parse(@tagName(tag) ++ ".0") catch unreachable,
-            };
-            i += 1;
-        }
-
-        break :blk build_runners;
-    };
 };