Fix build on riscv32 (#675)

absl/base/internal/direct_mmap.h

@@ -61,6 +61,10 @@ extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
 #endif
 #endif  // __BIONIC__
 
+#if defined(__NR_mmap2) && !defined(SYS_mmap2)
+#define SYS_mmap2 __NR_mmap2
+#endif
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
@@ -72,6 +76,7 @@ inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
 #if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__) || \
     (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) ||                   \
     (defined(__PPC__) && !defined(__PPC64__)) ||                             \
+    (defined(__riscv) && __riscv_xlen == 32) ||                              \
     (defined(__s390__) && !defined(__s390x__))
   // On these architectures, implement mmap with mmap2.
   static int pagesize = 0;

absl/base/internal/spinlock_linux.inc

@@ -46,6 +46,14 @@ static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
 #endif
 #endif
 
+#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
+#define SYS_futex_time64 __NR_futex_time64
+#endif
+
+#if defined(SYS_futex_time64) && !defined(SYS_futex)
+#define SYS_futex SYS_futex_time64
+#endif
+
 extern "C" {
 
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(

absl/synchronization/internal/waiter.cc

@@ -86,6 +86,14 @@ static void MaybeBecomeIdle() {
 #endif
 #endif
 
+#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
+#define SYS_futex_time64 __NR_futex_time64
+#endif
+
+#if defined(SYS_futex_time64) && !defined(SYS_futex)
+#define SYS_futex SYS_futex_time64
+#endif
+
 class Futex {
  public:
   static int WaitUntil(std::atomic<int32_t> *v, int32_t val,