add riscv64 architecture support

Author: Alex Suykov <alex.suykov@gmail.com>
Author: Aric Belsito <lluixhi@gmail.com>
Author: Drew DeVault <sir@cmpwn.com>
Author: Michael Clark <mjc@sifive.com>
Author: Michael Forney <mforney@mforney.org>
Author: Stefan O'Rear <sorear2@gmail.com>

This port has involved the work of many people over several years. I
have tried to ensure that everyone with substantial contributions has
been credited above; if any omissions are found they will be noted
later in an update to the authors/contributors list in the COPYRIGHT
file.

The version committed here comes from the riscv/riscv-musl repo's
commit 3fe7e2c75df78eef42dcdc352a55757729f451e2, with minor changes by
me for issues found during final review:

- a_ll/a_sc atomics are removed (according to the ISA spec, lr/sc
  are not safe to use in separate inline asm fragments)

- a_cas[_p] is fixed to be a memory barrier

- the call from the _start assembly into the C part of crt1/ldso is
  changed to allow for the possibility that the linker does not place
  them nearby each other.

- DTP_OFFSET is defined correctly so that local-dynamic TLS works

- reloc.h LDSO_ARCH logic is simplified and made explicit.

- unused, non-functional crti/n asm files are removed.

- an empty .sdata section is added to crt1 so that the
  __global_pointer reference is resolvable.

- indentation style errors in some asm files are fixed.

1 files changed, 112 insertions, 0 deletions

diff --git a/arch/riscv64/bits/signal.h b/arch/riscv64/bits/signal.h
new file mode 100644
index 00000000..4c94a8f0
--- /dev/null
+++ b/arch/riscv64/bits/signal.h
@@ -0,0 +1,112 @@
+#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+
+#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+# define MINSIGSTKSZ 2048
+# define SIGSTKSZ 8192
+#endif
+
+/* gregs[0] holds the program counter. */
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+typedef unsigned long greg_t;
+typedef unsigned long gregset_t[32];
+
+struct __riscv_f_ext_state {
+	unsigned int f[32];
+	unsigned int fcsr;
+};
+
+struct __riscv_d_ext_state {
+	unsigned long long f[32];
+	unsigned int fcsr;
+};
+
+struct __riscv_q_ext_state {
+	unsigned long long f[64] __attribute__((aligned(16)));
+	unsigned int fcsr;
+	unsigned int reserved[3];
+};
+
+union __riscv_fp_state {
+	struct __riscv_f_ext_state f;
+	struct __riscv_d_ext_state d;
+	struct __riscv_q_ext_state q;
+};
+
+typedef union __riscv_fp_state fpregset_t;
+
+typedef struct sigcontext {
+	gregset_t gregs;
+	fpregset_t fpregs;
+} mcontext_t;
+
+#else
+typedef struct {
+	unsigned long gregs[32];
+	unsigned long long fpregs[66];
+} mcontext_t;
+#endif
+
+struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+};
+
+typedef struct __ucontext
+{
+	unsigned long uc_flags;
+	struct __ucontext *uc_link;
+	stack_t uc_stack;
+	sigset_t uc_sigmask;
+	mcontext_t uc_mcontext;
+} ucontext_t;
+
+#define SA_NOCLDSTOP 1
+#define SA_NOCLDWAIT 2
+#define SA_SIGINFO   4
+#define SA_ONSTACK   0x08000000
+#define SA_RESTART   0x10000000
+#define SA_NODEFER   0x40000000
+#define SA_RESETHAND 0x80000000
+#define SA_RESTORER  0x04000000
+
+#endif
+
+#define SIGHUP     1
+#define SIGINT     2
+#define SIGQUIT    3
+#define SIGILL     4
+#define SIGTRAP    5
+#define SIGABRT    6
+#define SIGIOT     SIGABRT
+#define SIGBUS     7
+#define SIGFPE     8
+#define SIGKILL    9
+#define SIGUSR1   10
+#define SIGSEGV   11
+#define SIGUSR2   12
+#define SIGPIPE   13
+#define SIGALRM   14
+#define SIGTERM   15
+#define SIGSTKFLT 16
+#define SIGCHLD   17
+#define SIGCONT   18
+#define SIGSTOP   19
+#define SIGTSTP   20
+#define SIGTTIN   21
+#define SIGTTOU   22
+#define SIGURG    23
+#define SIGXCPU   24
+#define SIGXFSZ   25
+#define SIGVTALRM 26
+#define SIGPROF   27
+#define SIGWINCH  28
+#define SIGIO     29
+#define SIGPOLL   SIGIO
+#define SIGPWR    30
+#define SIGSYS    31
+#define SIGUNUSED SIGSYS
+
+#define _NSIG     65