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, 56 insertions, 0 deletions

diff --git a/include/elf.h b/include/elf.h
index aad522e4..41e6e0c3 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -3226,6 +3226,62 @@ enum
 #define R_BPF_NONE		0
 #define R_BPF_MAP_FD		1
 
+#define R_RISCV_NONE            0
+#define R_RISCV_32              1
+#define R_RISCV_64              2
+#define R_RISCV_RELATIVE        3
+#define R_RISCV_COPY            4
+#define R_RISCV_JUMP_SLOT       5
+#define R_RISCV_TLS_DTPMOD32    6
+#define R_RISCV_TLS_DTPMOD64    7
+#define R_RISCV_TLS_DTPREL32    8
+#define R_RISCV_TLS_DTPREL64    9
+#define R_RISCV_TLS_TPREL32     10
+#define R_RISCV_TLS_TPREL64     11
+
+#define R_RISCV_BRANCH          16
+#define R_RISCV_JAL             17
+#define R_RISCV_CALL            18
+#define R_RISCV_CALL_PLT        19
+#define R_RISCV_GOT_HI20        20
+#define R_RISCV_TLS_GOT_HI20    21
+#define R_RISCV_TLS_GD_HI20     22
+#define R_RISCV_PCREL_HI20      23
+#define R_RISCV_PCREL_LO12_I    24
+#define R_RISCV_PCREL_LO12_S    25
+#define R_RISCV_HI20            26
+#define R_RISCV_LO12_I          27
+#define R_RISCV_LO12_S          28
+#define R_RISCV_TPREL_HI20      29
+#define R_RISCV_TPREL_LO12_I    30
+#define R_RISCV_TPREL_LO12_S    31
+#define R_RISCV_TPREL_ADD       32
+#define R_RISCV_ADD8            33
+#define R_RISCV_ADD16           34
+#define R_RISCV_ADD32           35
+#define R_RISCV_ADD64           36
+#define R_RISCV_SUB8            37
+#define R_RISCV_SUB16           38
+#define R_RISCV_SUB32           39
+#define R_RISCV_SUB64           40
+#define R_RISCV_GNU_VTINHERIT   41
+#define R_RISCV_GNU_VTENTRY     42
+#define R_RISCV_ALIGN           43
+#define R_RISCV_RVC_BRANCH      44
+#define R_RISCV_RVC_JUMP        45
+#define R_RISCV_RVC_LUI         46
+#define R_RISCV_GPREL_I         47
+#define R_RISCV_GPREL_S         48
+#define R_RISCV_TPREL_I         49
+#define R_RISCV_TPREL_S         50
+#define R_RISCV_RELAX           51
+#define R_RISCV_SUB6            52
+#define R_RISCV_SET6            53
+#define R_RISCV_SET8            54
+#define R_RISCV_SET16           55
+#define R_RISCV_SET32           56
+#define R_RISCV_32_PCREL        57
+
 #ifdef __cplusplus
 }
 #endif