[PATCH] elf.h: Add ELFCOMPRESS_ZSTD

[Fangrui Song <maskray@google.com>]

Link: https://sourceware.org/pipermail/gnu-gabi/2022q2/000498.html ("New ch_type value ELFCOMPRESS_ZSTD?")
Link: https://groups.google.com/g/generic-abi/c/satyPkuMisk ("Add new ch_type value: ELFCOMPRESS_ZSTD")

---

I wish that the macro definition can catch up the upcoming
https://sourceware.org/glibc/wiki/Release/2.36 [1], so that
projects can expect the value ELFCOMPRESS_ZSTD from elf.h.
The projects may choose to define the macro themselves,
but having the definition in an earlier release seems a good idea
anyway, and it the glibc definition makes it clearer ELFCOMPRESS_ZSTD
is standard and vendors can start adding support.

[1]: https://sourceware.org/pipermail/libc-alpha/2022-July/140352.html
("Release of glibc 2.36 in 1 month! Please add blockers and desirable for release.")

From https://groups.google.com/g/generic-abi/c/9OO5vhxb00Y ("Ongoing Maintenance of the gABI"),
we should be able to define this once Cary agrees.
---
 elf/elf.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/elf/elf.h b/elf/elf.h
index 2b5c2c5fb6..f6ae2348a9 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -505,6 +505,7 @@ typedef struct
 
 /* Legal values for ch_type (compression algorithm).  */
 #define ELFCOMPRESS_ZLIB	1	   /* ZLIB/DEFLATE algorithm.  */
+#define ELFCOMPRESS_ZSTD	2	   /* Zstandard algorithm.  */
 #define ELFCOMPRESS_LOOS	0x60000000 /* Start of OS-specific.  */
 #define ELFCOMPRESS_HIOS	0x6fffffff /* End of OS-specific.  */
 #define ELFCOMPRESS_LOPROC	0x70000000 /* Start of processor-specific.  */
-- 
2.37.0.144.g8ac04bfd2-goog