Add a missing riscv64 psabi constant.

Also group all the RELR/arm64/riscv64 bits together rather than mixing them up slightly as we'd done so far.

Change-Id: Iff1ea2cfca9ff702b88aa2e7d09db46e2f34f965
diff --git a/libc/include/elf.h b/libc/include/elf.h
index 1275f2e..374d5bb 100644
--- a/libc/include/elf.h
+++ b/libc/include/elf.h
@@ -223,8 +223,6 @@
 #undef SHT_NUM
 #define SHT_NUM 20
 
-#define SHT_RISCV_ATTRIBUTES 0x70000003
-
 /*
  * Experimental support for SHT_RELR sections. For details, see proposal
  * at https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg.
@@ -254,6 +252,8 @@
 #define DT_ANDROID_RELA 0x60000011 // DT_LOOS + 4
 #define DT_ANDROID_RELASZ 0x60000012 // DT_LOOS + 5
 
+/* arm64 psabi. */
+
 /* TODO: upstreamed to FreeBSD as https://github.com/freebsd/freebsd-src/pull/1141/. */
 #define DT_AARCH64_MEMTAG_MODE 0x70000009
 #define DT_AARCH64_MEMTAG_HEAP 0x7000000b
@@ -270,6 +270,8 @@
 #define R_ARM_TLS_DESC 13
 #define R_ARM_IRELATIVE 160
 
+/* riscv64 psabi. */
+
 /* FreeBSD is missing these, found in
  * https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#relocations
  * so I've sent https://github.com/freebsd/freebsd-src/pull/1141 upstream.
@@ -283,6 +285,12 @@
 #define R_RISCV_TLSDESC_ADD_LO12 64
 #define R_RISCV_TLSDESC_CALL 65
 
+/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#program-header-table */
+#define PT_RISCV_ATTRIBUTES 0x70000003
+
+/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#section-types */
+#define SHT_RISCV_ATTRIBUTES 0x70000003
+
 /* FreeBSD spells this slightly differently to Linux. Linux is correct according to
  * https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#file-header
  * so I've sent https://github.com/freebsd/freebsd-src/pull/1148 upstream.