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/arch-mips/bionic/syscall.S b/libc/arch-mips/bionic/syscall.S
index 5fed0ac..857bbab 100644
--- a/libc/arch-mips/bionic/syscall.S
+++ b/libc/arch-mips/bionic/syscall.S
@@ -36,26 +36,26 @@
 
 ENTRY(syscall)
     .set noreorder
-    .cpload t9
-    move    v0, a0
-    move    a0, a1
-    move    a1, a2
-    move    a2, a3
-    lw      a3, 16(sp)
-    lw      t0, 20(sp)
-    lw      t1, 24(sp)
-    subu    sp, STACKSIZE
-    sw      t0, 16(sp)
-    sw      t1, 20(sp)
+    .cpload $t9
+    move    $v0, $a0
+    move    $a0, $a1
+    move    $a1, $a2
+    move    $a2, $a3
+    lw      $a3, 16($sp)
+    lw      $t0, 20($sp)
+    lw      $t1, 24($sp)
+    subu    $sp, STACKSIZE
+    sw      $t0, 16($sp)
+    sw      $t1, 20($sp)
     syscall
-    addu    sp, STACKSIZE
-    bnez    a3, 1f
-    move    a0, v0
-    j       ra
+    addu    $sp, STACKSIZE
+    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(syscall)