uapi headers: simplify the <linux/compiler.h> stuff.

We don't really need <linux/compiler.h> and <linux/compiler_types.h>. We
already have a mechanism to remove unused macros, so let's do that. We
don't currently have a way to remove unused #includes, so we still need
<linux/compiler.h> and <linux/compiler_types.h> files (but I've clarified
the comments in them).

I've kept the empty definitions of `__user` and `__force` for source
compatibility. (We had one security test at least that was assuming
a kernel struct definition will "just work".)

Bug: http://b/262917450
Test: treehugger
Change-Id: Iacbbbc1aeef9a4fac52dabd7811ab875cc267d4f
diff --git a/libc/kernel/uapi/asm-generic/poll.h b/libc/kernel/uapi/asm-generic/poll.h
index 372bc77..ba6f2e9 100644
--- a/libc/kernel/uapi/asm-generic/poll.h
+++ b/libc/kernel/uapi/asm-generic/poll.h
@@ -41,8 +41,8 @@
 #ifndef POLLRDHUP
 #define POLLRDHUP 0x2000
 #endif
-#define POLLFREE (__force __poll_t) 0x4000
-#define POLL_BUSY_LOOP (__force __poll_t) 0x8000
+#define POLLFREE ( __poll_t) 0x4000
+#define POLL_BUSY_LOOP ( __poll_t) 0x8000
 struct pollfd {
   int fd;
   short events;
diff --git a/libc/kernel/uapi/asm-generic/siginfo.h b/libc/kernel/uapi/asm-generic/siginfo.h
index c5e4178..90393ba 100644
--- a/libc/kernel/uapi/asm-generic/siginfo.h
+++ b/libc/kernel/uapi/asm-generic/siginfo.h
@@ -22,7 +22,7 @@
 #include <linux/types.h>
 typedef union sigval {
   int sival_int;
-  void __user * sival_ptr;
+  void  * sival_ptr;
 } sigval_t;
 #define SI_MAX_SIZE 128
 #ifndef __ARCH_SI_BAND_T
@@ -58,7 +58,7 @@
     __ARCH_SI_CLOCK_T _stime;
   } _sigchld;
   struct {
-    void __user * _addr;
+    void  * _addr;
 #ifdef __ia64__
     int _imm;
     unsigned int _flags;
@@ -70,8 +70,8 @@
       short _addr_lsb;
       struct {
         char _dummy_bnd[__ADDR_BND_PKEY_PAD];
-        void __user * _lower;
-        void __user * _upper;
+        void  * _lower;
+        void  * _upper;
       } _addr_bnd;
       struct {
         char _dummy_pkey[__ADDR_BND_PKEY_PAD];
@@ -89,7 +89,7 @@
     int _fd;
   } _sigpoll;
   struct {
-    void __user * _call_addr;
+    void  * _call_addr;
     int _syscall;
     unsigned int _arch;
   } _sigsys;
diff --git a/libc/kernel/uapi/asm-generic/signal-defs.h b/libc/kernel/uapi/asm-generic/signal-defs.h
index c7e9504..dea8fbc 100644
--- a/libc/kernel/uapi/asm-generic/signal-defs.h
+++ b/libc/kernel/uapi/asm-generic/signal-defs.h
@@ -55,11 +55,11 @@
 #endif
 #ifndef __ASSEMBLY__
 typedef void __signalfn_t(int);
-typedef __signalfn_t __user * __sighandler_t;
+typedef __signalfn_t  * __sighandler_t;
 typedef void __restorefn_t(void);
-typedef __restorefn_t __user * __sigrestore_t;
-#define SIG_DFL ((__force __sighandler_t) 0)
-#define SIG_IGN ((__force __sighandler_t) 1)
-#define SIG_ERR ((__force __sighandler_t) - 1)
+typedef __restorefn_t  * __sigrestore_t;
+#define SIG_DFL (( __sighandler_t) 0)
+#define SIG_IGN (( __sighandler_t) 1)
+#define SIG_ERR (( __sighandler_t) - 1)
 #endif
 #endif
diff --git a/libc/kernel/uapi/asm-generic/signal.h b/libc/kernel/uapi/asm-generic/signal.h
index 5cb1dce..9cf393f 100644
--- a/libc/kernel/uapi/asm-generic/signal.h
+++ b/libc/kernel/uapi/asm-generic/signal.h
@@ -82,7 +82,7 @@
   sigset_t sa_mask;
 };
 typedef struct sigaltstack {
-  void __user * ss_sp;
+  void  * ss_sp;
   int ss_flags;
   __kernel_size_t ss_size;
 } stack_t;