Clarify one of the "missing" FreeBSD ELF constants.

Test: treehugger
Change-Id: I7173ac704e6537a4e99a976baec46aa22df751bd
diff --git a/libc/include/elf.h b/libc/include/elf.h
index 1dfc008..04a73f7 100644
--- a/libc/include/elf.h
+++ b/libc/include/elf.h
@@ -266,4 +266,6 @@
 /* TODO: upstream these to FreeBSD? */
 #define R_ARM_TLS_DESC 13
 #define R_ARM_IRELATIVE 160
-#define R_X86_64_JUMP_SLOT 7
+
+/* BSD spells this slightly differently to Linux. */
+#define R_X86_64_JUMP_SLOT R_X86_64_JMP_SLOT