std.c reorganization

It is now composed of these main sections:
* Declarations that are shared among all operating systems.
* Declarations that have the same name, but different type signatures
  depending on the operating system. Often multiple operating systems
  share the same type signatures however.
* Declarations that are specific to a single operating system.
  - These are imported one per line so you can see where they come from,
    protected by a comptime block to prevent accessing the wrong one.

Closes #19352 by changing the convention to making types `void` and
functions `{}`, so that it becomes possible to update `@hasDecl` sites
to use `@TypeOf(f) != void` or `T != void`. Happily, this ended up
removing some duplicate logic and update some bitrotted feature
detection checks.

A handful of types have been modified to gain namespacing and type
safety. This is a breaking change.

Oh, and the last usage of `usingnamespace` site is eliminated.

1 files changed, 10 insertions, 4 deletions

diff --git a/lib/std/os/linux/mips.zig b/lib/std/os/linux/mips.zig
index 03098a7d1c..1b83194933 100644
--- a/lib/std/os/linux/mips.zig
+++ b/lib/std/os/linux/mips.zig
@@ -326,13 +326,13 @@ pub const Stat = extern struct {
 };
 
 pub const timeval = extern struct {
-    tv_sec: isize,
-    tv_usec: isize,
+    sec: isize,
+    usec: isize,
 };
 
 pub const timezone = extern struct {
-    tz_minuteswest: i32,
-    tz_dsttime: i32,
+    minuteswest: i32,
+    dsttime: i32,
 };
 
 pub const Elf_Symndx = u32;
@@ -396,3 +396,9 @@ pub const rlimit_resource = enum(c_int) {
 
     _,
 };
+
+/// TODO
+pub const ucontext_t = void;
+
+/// TODO
+pub const getcontext = {};