extend/ENV/super: allow bottles with custom architectures

Currently, Homebrew recognises only the architectures listed in
`hardware.rb`. [1] Attempting to pass an unrecognised architecture to
`--bottle-arch` while building a bottle returns an error.

Let's change that by passing unrecognised bottle arches to the compiler
instead of immediately failing with a `CannotInstallFormulaError`.

Partially resolves #5815.

[1] 64b6846d60/Library/Homebrew/hardware.rb (L28-L42)

Library/Homebrew/extend/ENV/super.rb

@@ -261,6 +261,9 @@ module Superenv
   sig { returns(String) }
   def determine_optflags
     Hardware::CPU.optimization_flags.fetch(effective_arch)
+  rescue KeyError
+    odebug "Building a bottle for custom architecture (#{effective_arch})..."
+    Hardware::CPU.arch_flag(effective_arch)
   end
 
   sig { returns(String) }

Library/Homebrew/formula_installer.rb

@@ -395,10 +395,6 @@ class FormulaInstaller
 
     return if only_deps?
 
-    if build_bottle? && (arch = @bottle_arch) && Hardware::CPU.optimization_flags.exclude?(arch.to_sym)
-      raise CannotInstallFormulaError, "Unrecognized architecture for --bottle-arch: #{arch}"
-    end
-
     formula.deprecated_flags.each do |deprecated_option|
       old_flag = deprecated_option.old_flag
       new_flag = deprecated_option.current_flag