arch/Config.in.x86: drop knightslanding and knightsmill archs

According to the GCC 14.x release notes at
https://gcc.gnu.org/gcc-14/changes.html:

  Xeon Phi CPUs support (a.k.a. Knight Landing and Knight Mill) are
  marked as deprecated. GCC will emit a warning when using the
  -mavx5124fmaps, -mavx5124vnniw, -mavx512er, -mavx512pf,
  -mprefetchwt1, -march=knl, -march=knm, -mtune=knl or -mtune=knm
  compiler switches. Support will be removed in GCC 15.

Using those architectures already emits warnings, which when treated
as errors cause build failures, such as:

  cc1: error: '-march=knm' support will be removed in GCC 15 [-Werror=deprecated]
  cc1: all warnings being treated as errors

Therefore, let's drop support for those two architectures, which are
anyway not common at all, especially in the embedded space.

Fixes:

  http://autobuild.buildroot.net/results/ce98c41b22212f52bf7b53d84871b8e03409dbca/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Config.in.legacy

@@ -146,6 +146,20 @@ endif
 
 comment "Legacy options removed in 2024.08"
 
+config BR2_x86_knightslanding
+	bool "knightslanding x86 architecture support dropped"
+	select BR2_LEGACY
+	help
+	  GCC 14.x has marked this architecture as obsolete, and emits
+	  a warning causing build failures.
+
+config BR2_x86_knightsmill
+	bool "knightsmill x86 architecture support dropped"
+	select BR2_LEGACY
+	help
+	  GCC 14.x has marked this architecture as obsolete, and emits
+	  a warning causing build failures.
+
 config BR2_PACKAGE_DVB_APPS
 	bool "dvb-apps package removed"
 	select BR2_LEGACY

arch/Config.in.x86

@@ -379,30 +379,6 @@ config BR2_x86_grandridge
 	select BR2_X86_CPU_HAS_AVX
 	select BR2_X86_CPU_HAS_AVX2
 	select BR2_ARCH_NEEDS_GCC_AT_LEAST_13
-config BR2_x86_knightslanding
-	bool "knightslanding"
-	select BR2_X86_CPU_HAS_MMX
-	select BR2_X86_CPU_HAS_SSE
-	select BR2_X86_CPU_HAS_SSE2
-	select BR2_X86_CPU_HAS_SSE3
-	select BR2_X86_CPU_HAS_SSSE3
-	select BR2_X86_CPU_HAS_SSE4
-	select BR2_X86_CPU_HAS_SSE42
-	select BR2_X86_CPU_HAS_AVX
-	select BR2_X86_CPU_HAS_AVX2
-	select BR2_ARCH_NEEDS_GCC_AT_LEAST_5
-config BR2_x86_knightsmill
-	bool "knightsmill"
-	select BR2_X86_CPU_HAS_MMX
-	select BR2_X86_CPU_HAS_SSE
-	select BR2_X86_CPU_HAS_SSE2
-	select BR2_X86_CPU_HAS_SSE3
-	select BR2_X86_CPU_HAS_SSSE3
-	select BR2_X86_CPU_HAS_SSE4
-	select BR2_X86_CPU_HAS_SSE42
-	select BR2_X86_CPU_HAS_AVX
-	select BR2_X86_CPU_HAS_AVX2
-	select BR2_ARCH_NEEDS_GCC_AT_LEAST_8
 config BR2_x86_skylake_avx512
 	bool "skylake-avx512"
 	select BR2_X86_CPU_HAS_MMX
@@ -791,8 +767,6 @@ config BR2_GCC_TARGET_ARCH
 	default "tremont"	if BR2_x86_tremont
 	default "sierraforest"	if BR2_x86_sierraforest
 	default "grandridge"	if BR2_x86_grandridge
-	default "knl"		if BR2_x86_knightslanding
-	default "knm"		if BR2_x86_knightsmill
 	default "skylake-avx512" if BR2_x86_skylake_avx512
 	default "cannonlake"	if BR2_x86_cannonlake
 	default "icelake-client" if BR2_x86_icelake_client