Unified sysroot: kill arch-specific include dirs.

<machine/asm.h> was internal use only.

<machine/fenv.h> is quite large, but can live in <bits/...>.

<machine/regdef.h> is trivially replaced by saying $x instead of x in
our assembler.

<machine/setjmp.h> is trivially inlined into <setjmp.h>.

<sgidefs.h> is unused.

Bug: N/A
Test: builds
Change-Id: Id05dbab43a2f9537486efb8f27a5ef167b055815
diff --git a/libc/tools/gensyscalls.py b/libc/tools/gensyscalls.py
index 46affb7..124dd72 100755
--- a/libc/tools/gensyscalls.py
+++ b/libc/tools/gensyscalls.py
@@ -118,16 +118,16 @@
 
 mips_call = syscall_stub_header + """\
     .set noreorder
-    .cpload t9
-    li v0, %(__NR_name)s
+    .cpload $t9
+    li $v0, %(__NR_name)s
     syscall
-    bnez a3, 1f
-    move a0, v0
-    j ra
+    bnez $a3, 1f
+    move $a0, $v0
+    j $ra
     nop
 1:
-    la t9,__set_errno_internal
-    j t9
+    la $t9,__set_errno_internal
+    j $t9
     nop
     .set reorder
 END(%(func)s)