Remove code for unsupported macOS versions

Library/Homebrew/brew.sh

@@ -603,7 +603,7 @@ then
   HOMEBREW_PRODUCT="Homebrew"
   HOMEBREW_SYSTEM="Macintosh"
   [[ "${HOMEBREW_PROCESSOR}" == "x86_64" ]] && HOMEBREW_PROCESSOR="Intel"
-  # Don't change this from Mac OS X to match what macOS itself does in Safari on 10.12
+  # Don't change this from Mac OS X to match what macOS itself does in Safari
   HOMEBREW_OS_USER_AGENT_VERSION="Mac OS X ${HOMEBREW_MACOS_VERSION}"
 
   if [[ "$(sysctl -n hw.optional.arm64 2>/dev/null)" == "1" ]]

Library/Homebrew/extend/os/mac/extend/ENV/super.rb

@@ -125,24 +125,6 @@ def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_a
 
         super
 
-        # Filter out symbols known not to be defined since GNU Autotools can't
-        # reliably figure this out with Xcode 8 and above.
-        if MacOS.version == "10.12" && MacOS::Xcode.version >= "9.0"
-          %w[fmemopen futimens open_memstream utimensat].each do |s|
-            ENV["ac_cv_func_#{s}"] = "no"
-          end
-        elsif MacOS.version == "10.11" && MacOS::Xcode.version >= "8.0"
-          %w[basename_r clock_getres clock_gettime clock_settime dirname_r
-             getentropy mkostemp mkostemps timingsafe_bcmp].each do |s|
-            ENV["ac_cv_func_#{s}"] = "no"
-          end
-
-          ENV["ac_cv_search_clock_gettime"] = "no"
-
-          # works around libev.m4 unsetting ac_cv_func_clock_gettime
-          ENV["ac_have_clock_syscall"] = "no"
-        end
-
         # On macOS Sonoma (at least release candidate), iconv() is generally
         # present and working, but has a minor regression that defeats the
         # test implemented in gettext's configure script (and used by many

Library/Homebrew/extend/os/mac/formula.rb

@@ -23,10 +23,6 @@ def valid_platform?
       def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework: "LAST")
         args = super
 
-        # Avoid false positives for clock_gettime support on 10.11.
-        # CMake cache entries for other weak symbols may be added here as needed.
-        args << "-DHAVE_CLOCK_GETTIME:INTERNAL=0" if MacOS.version == "10.11" && MacOS::Xcode.version >= "8.0"
-
         # Ensure CMake is using the same SDK we are using.
         args << "-DCMAKE_OSX_SYSROOT=#{T.must(MacOS.sdk_for_formula(self)).path}" if MacOS.sdk_root_needed?