mm: fold arch_randomize_brk into ARCH_HAS_ELF_RANDOMIZE

The arch_randomize_brk() function is used on several architectures,
even those that don't support ET_DYN ASLR. To avoid bulky extern/#define
tricks, consolidate the support under CONFIG_ARCH_HAS_ELF_RANDOMIZE for
the architectures that support it, while still handling CONFIG_COMPAT_BRK.

Signed-off-by: Kees Cook <[email protected]>
Cc: Hector Marco-Gisbert <[email protected]>
Cc: Russell King <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: "David A. Long" <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Arun Chandran <[email protected]>
Cc: Yann Droneaud <[email protected]>
Cc: Min-Hua Chen <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Alex Smith <[email protected]>
Cc: Markos Chandras <[email protected]>
Cc: Vineeth Vijayan <[email protected]>
Cc: Jeff Bailey <[email protected]>
Cc: Michael Holzheu <[email protected]>
Cc: Ben Hutchings <[email protected]>
Cc: Behan Webster <[email protected]>
Cc: Ismael Ripoll <[email protected]>
Cc: Jan-Simon Mller <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/Kconfig

@@ -497,6 +497,7 @@ config ARCH_HAS_ELF_RANDOMIZE
 	  An architecture supports choosing randomized locations for
 	  stack, mmap, brk, and ET_DYN. Defined functions:
 	  - arch_mmap_rnd()
+	  - arch_randomize_brk()
 
 #
 # ABI hall of shame