Remove #include <asm/unistd.h> from linux_syscall_ranges.h and syscall.cc.

The header is included for __NR_SYSCALL_BASE and __ARM_NR_BASE.
Some toolchain (in particular, PNaCl toolchain) does not provide
asm/unistd.h (so that neither __NR_SYSCALL_BASE nor __ARM_NR_BASE
is provided).
This CL removes the dependency to asm/unistd.h from linux_syscall_ranges.h,
instead define the values if necessary.

Also, this CL removes the include from syscall.cc, too, which is
unused.

TEST=Ran bots.
BUG=358465

Review URL: https://codereview.chromium.org/1071653002

Cr-Commit-Position: refs/heads/master@{#324371}

sandbox/linux/bpf_dsl/linux_syscall_ranges.h

@@ -5,8 +5,6 @@
 #ifndef SANDBOX_LINUX_BPF_DSL_LINUX_SYSCALL_RANGES_H_
 #define SANDBOX_LINUX_BPF_DSL_LINUX_SYSCALL_RANGES_H_
 
-#include <asm/unistd.h>  // For __NR_SYSCALL_BASE
-
 #if defined(__x86_64__)
 
 #define MIN_SYSCALL         0u
@@ -25,15 +23,19 @@
 // and a "ghost syscall private to the kernel", cmpxchg,
 // at |__ARM_NR_BASE+0x00fff0|.
 // See </arch/arm/include/asm/unistd.h> in the Linux kernel.
-#define MIN_SYSCALL         ((unsigned int)__NR_SYSCALL_BASE)
+
+// __NR_SYSCALL_BASE is 0 in thumb and ARM EABI.
+#define MIN_SYSCALL         0u
 #define MAX_PUBLIC_SYSCALL  (MIN_SYSCALL + 1024u)
-#define MIN_PRIVATE_SYSCALL ((unsigned int)__ARM_NR_BASE)
+// __ARM_NR_BASE is __NR_SYSCALL_BASE + 0xf0000u
+#define MIN_PRIVATE_SYSCALL 0xf0000u
 #define MAX_PRIVATE_SYSCALL (MIN_PRIVATE_SYSCALL + 16u)
-#define MIN_GHOST_SYSCALL   ((unsigned int)__ARM_NR_BASE + 0xfff0u)
+#define MIN_GHOST_SYSCALL   (MIN_PRIVATE_SYSCALL + 0xfff0u)
 #define MAX_SYSCALL         (MIN_GHOST_SYSCALL + 4u)
 
 #elif defined(__mips__) && (_MIPS_SIM == _ABIO32)
 
+#include <asm/unistd.h>  // for __NR_O32_Linux and __NR_Linux_syscalls
 #define MIN_SYSCALL         __NR_O32_Linux
 #define MAX_PUBLIC_SYSCALL  (MIN_SYSCALL + __NR_Linux_syscalls)
 #define MAX_SYSCALL         MAX_PUBLIC_SYSCALL

sandbox/linux/seccomp-bpf/syscall.cc

@@ -4,7 +4,6 @@
 
 #include "sandbox/linux/seccomp-bpf/syscall.h"
 
-#include <asm/unistd.h>
 #include <errno.h>
 #include <stdint.h>