Fix sigaction(3) for 64-bit.

Also clean up <signal.h> and revert the hacks that were necessary
for 64-bit in linker/debugger.cpp until now.

Change-Id: I3b0554ca8a49ee1c97cda086ce2c1954ebc11892
diff --git a/libc/arch-mips/syscalls.mk b/libc/arch-mips/syscalls.mk
index 4e7b65b..fc96222 100644
--- a/libc/arch-mips/syscalls.mk
+++ b/libc/arch-mips/syscalls.mk
@@ -22,6 +22,7 @@
 syscall_src += arch-mips/syscalls/__rt_sigtimedwait.S
 syscall_src += arch-mips/syscalls/__sched_getaffinity.S
 syscall_src += arch-mips/syscalls/__set_thread_area.S
+syscall_src += arch-mips/syscalls/__sigaction.S
 syscall_src += arch-mips/syscalls/__statfs64.S
 syscall_src += arch-mips/syscalls/__sys_clone.S
 syscall_src += arch-mips/syscalls/__syslog.S
@@ -179,7 +180,6 @@
 syscall_src += arch-mips/syscalls/setuid.S
 syscall_src += arch-mips/syscalls/setxattr.S
 syscall_src += arch-mips/syscalls/shutdown.S
-syscall_src += arch-mips/syscalls/sigaction.S
 syscall_src += arch-mips/syscalls/sigaltstack.S
 syscall_src += arch-mips/syscalls/signalfd4.S
 syscall_src += arch-mips/syscalls/socket.S
diff --git a/libc/arch-mips/syscalls/sigaction.S b/libc/arch-mips/syscalls/__sigaction.S
similarity index 78%
rename from libc/arch-mips/syscalls/sigaction.S
rename to libc/arch-mips/syscalls/__sigaction.S
index d1808c6..cc53ab4 100644
--- a/libc/arch-mips/syscalls/sigaction.S
+++ b/libc/arch-mips/syscalls/__sigaction.S
@@ -2,11 +2,11 @@
 
 #include <asm/unistd.h>
     .text
-    .globl sigaction
+    .globl __sigaction
     .align 4
-    .ent sigaction
+    .ent __sigaction
 
-sigaction:
+__sigaction:
     .set noreorder
     .cpload $t9
     li $v0, __NR_sigaction
@@ -20,4 +20,4 @@
     j $t9
     nop
     .set reorder
-    .end sigaction
+    .end __sigaction