std.Build: Remove unused c_std field

This field has not been referenced by compile steps since
e76ce2c, all the way back in 2019.
To specify the language standard, pass `-std=[value]` as a regular
C flag instead.

Author: castholm

lib/std/Build.zig

@@ -193,12 +193,6 @@ pub const PkgConfigPkg = struct {
     desc: []const u8,
 };
 
-pub const CStd = enum {
-    C89,
-    C99,
-    C11,
-};
-
 const UserInputOptionsMap = StringHashMap(UserInputOption);
 const AvailableOptionsMap = StringHashMap(AvailableOption);
 

lib/std/Build/Module.zig

@@ -19,7 +19,6 @@ include_dirs: std.ArrayListUnmanaged(IncludeDir),
 lib_paths: std.ArrayListUnmanaged(LazyPath),
 rpaths: std.ArrayListUnmanaged(RPath),
 frameworks: std.StringArrayHashMapUnmanaged(LinkFrameworkOptions),
-c_std: std.Build.CStd,
 link_objects: std.ArrayListUnmanaged(LinkObject),
 
 strip: ?bool,
@@ -164,7 +163,6 @@ pub const CreateOptions = struct {
     strip: ?bool = null,
     unwind_tables: ?bool = null,
     dwarf_format: ?std.dwarf.Format = null,
-    c_std: std.Build.CStd = .C99,
     code_model: std.builtin.CodeModel = .default,
     stack_protector: ?bool = null,
     stack_check: ?bool = null,
@@ -204,7 +202,6 @@ pub fn init(m: *Module, owner: *std.Build, options: CreateOptions, compile: ?*St
         .lib_paths = .{},
         .rpaths = .{},
         .frameworks = .{},
-        .c_std = options.c_std,
         .link_objects = .{},
         .strip = options.strip,
         .unwind_tables = options.unwind_tables,