std.os.linux: Fix MIPS signal numbers

Dunno why the MIPS signal numbers are different, or why Zig had them
already special cased, but wrong.

We have the technology to test these constants.  We should use it.

Author: rootbeer

lib/std/os/linux.zig

@@ -3499,40 +3499,40 @@ pub const SIG = if (is_mips) struct {
     pub const UNBLOCK = 2;
     pub const SETMASK = 3;
 
+    // https://github.com/torvalds/linux/blob/ca91b9500108d4cf083a635c2e11c884d5dd20ea/arch/mips/include/uapi/asm/signal.h#L25
     pub const HUP = 1;
     pub const INT = 2;
     pub const QUIT = 3;
     pub const ILL = 4;
     pub const TRAP = 5;
     pub const ABRT = 6;
     pub const IOT = ABRT;
-    pub const BUS = 7;
+    pub const EMT = 7;
     pub const FPE = 8;
     pub const KILL = 9;
-    pub const USR1 = 10;
+    pub const BUS = 10;
     pub const SEGV = 11;
-    pub const USR2 = 12;
+    pub const SYS = 12;
     pub const PIPE = 13;
     pub const ALRM = 14;
     pub const TERM = 15;
-    pub const STKFLT = 16;
-    pub const CHLD = 17;
-    pub const CONT = 18;
-    pub const STOP = 19;
-    pub const TSTP = 20;
-    pub const TTIN = 21;
-    pub const TTOU = 22;
-    pub const URG = 23;
-    pub const XCPU = 24;
-    pub const XFSZ = 25;
-    pub const VTALRM = 26;
-    pub const PROF = 27;
-    pub const WINCH = 28;
-    pub const IO = 29;
-    pub const POLL = 29;
-    pub const PWR = 30;
-    pub const SYS = 31;
-    pub const UNUSED = SIG.SYS;
+    pub const USR1 = 16;
+    pub const USR2 = 17;
+    pub const CHLD = 18;
+    pub const PWR = 19;
+    pub const WINCH = 20;
+    pub const URG = 21;
+    pub const IO = 22;
+    pub const POLL = IO;
+    pub const STOP = 23;
+    pub const TSTP = 24;
+    pub const CONT = 25;
+    pub const TTIN = 26;
+    pub const TTOU = 27;
+    pub const VTALRM = 28;
+    pub const PROF = 29;
+    pub const XCPU = 30;
+    pub const XFZ = 31;
 
     pub const ERR: ?Sigaction.handler_fn = @ptrFromInt(maxInt(usize));
     pub const DFL: ?Sigaction.handler_fn = @ptrFromInt(0);