x86/mpx: remove build infrastructure

From: Dave Hansen <dave.hansen@linux.intel.com>

MPX is being removed from the kernel due to a lack of support
in the toolchain going forward (gcc).

Remove the Kconfig option and the Makefile line.  This makes
arch/x86/mm/mpx.c and anything under an #ifdef for
X86_INTEL_MPX dead code.

Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

arch/x86/Kconfig

@@ -1896,34 +1896,6 @@ config X86_INTEL_UMIP
 	  specific cases in protected and virtual-8086 modes. Emulated
 	  results are dummy.
 
-config X86_INTEL_MPX
-	prompt "Intel MPX (Memory Protection Extensions)"
-	def_bool n
-	# Note: only available in 64-bit mode due to VMA flags shortage
-	depends on CPU_SUP_INTEL && X86_64
-	select ARCH_USES_HIGH_VMA_FLAGS
-	---help---
-	  MPX provides hardware features that can be used in
-	  conjunction with compiler-instrumented code to check
-	  memory references.  It is designed to detect buffer
-	  overflow or underflow bugs.
-
-	  This option enables running applications which are
-	  instrumented or otherwise use MPX.  It does not use MPX
-	  itself inside the kernel or to protect the kernel
-	  against bad memory references.
-
-	  Enabling this option will make the kernel larger:
-	  ~8k of kernel text and 36 bytes of data on a 64-bit
-	  defconfig.  It adds a long to the 'mm_struct' which
-	  will increase the kernel memory overhead of each
-	  process and adds some branches to paths used during
-	  exec() and munmap().
-
-	  For details, see Documentation/x86/intel_mpx.rst
-
-	  If unsure, say N.
-
 config X86_INTEL_MEMORY_PROTECTION_KEYS
 	prompt "Intel Memory Protection Keys"
 	def_bool y

arch/x86/mm/Makefile

@@ -45,7 +45,6 @@ obj-$(CONFIG_AMD_NUMA)		+= amdtopology.o
 obj-$(CONFIG_ACPI_NUMA)		+= srat.o
 obj-$(CONFIG_NUMA_EMU)		+= numa_emulation.o
 
-obj-$(CONFIG_X86_INTEL_MPX)			+= mpx.o
 obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS)	+= pkeys.o
 obj-$(CONFIG_RANDOMIZE_MEMORY)			+= kaslr.o
 obj-$(CONFIG_PAGE_TABLE_ISOLATION)		+= pti.o