www/qt5-webengine: Fix build with gperf >= 3.2

Blink was making no longer needed substitutions to the generated code
adding extra [[fallthrough]] attributes which caused build errors.

Thanks to dinoex for working through this with me.

Obtained from:	Gentoo

www/qt5-webengine/files/patch-src_3rdparty_chromium_third__party_blink_renderer_build_scripts_gperf.py

@@ -0,0 +1,27 @@
+--- src/3rdparty/chromium/third_party/blink/renderer/build/scripts/gperf.py.orig	2025-03-06 09:26:10 UTC
++++ src/3rdparty/chromium/third_party/blink/renderer/build/scripts/gperf.py
+@@ -29,24 +29,6 @@ def generate_gperf(gperf_path, gperf_input, gperf_args
+             stdout=subprocess.PIPE,
+             universal_newlines=True)
+         gperf_output = gperf.communicate(gperf_input)[0]
+-        # Massage gperf output to be more palatable for modern compilers.
+-        # TODO(thakis): Upstream these to gperf so we don't need massaging.
+-        # `register` is deprecated in C++11 and removed in C++17, so remove
+-        # it from gperf's output.
+-        # https://savannah.gnu.org/bugs/index.php?53028
+-        gperf_output = re.sub(r'\bregister ', '', gperf_output)
+-        # -Wimplicit-fallthrough needs an explicit fallthrough statement,
+-        # so replace gperf's /*FALLTHROUGH*/ comment with the statement.
+-        # https://savannah.gnu.org/bugs/index.php?53029
+-        gperf_output = gperf_output.replace('/*FALLTHROUGH*/',
+-                                            '  FALLTHROUGH;')
+-        # -Wpointer-to-int-cast warns about casting pointers to smaller ints
+-        # Replace {(int)(long)&(foo), bar} with
+-        # {static_cast<int>(reinterpret_cast<uintptr_t>(&(foo)), bar}
+-        gperf_output = re.sub(
+-            r'\(int\)\(long\)(.*?),',
+-            r'static_cast<int>(reinterpret_cast<uintptr_t>(\1)),',
+-            gperf_output)
+         script = 'third_party/blink/renderer/build/scripts/gperf.py'
+         return '// Generated by %s\n' % script + gperf_output
+     except OSError: