SCons: Re-allow upcoming GCC 8.4, fixes C++17 copy elision

Follow-up to godotengine#36484.

The patches for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86521 have now
landed in the `releases/gcc-8` branch and will be in GCC 8.4.

SConstruct

@@ -334,23 +334,25 @@ if selected_platform in platform_list:
 
     # Enforce our minimal compiler version requirements
     version = methods.get_compiler_version(env)
-    major = int(version[0]) if version is not None else -1
-    if methods.using_gcc(env):
-        # GCC 8 has a regression in the support of guaranteed copy elision
+    if version is not None and methods.using_gcc(env):
+        major = int(version[0])
+        minor = int(version[1])
+        # GCC 8 before 8.4 has a regression in the support of guaranteed copy elision
         # which causes a build failure: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86521
-        if major == 8:
-            print("Detected GCC version 8, which is not supported due to a regression "
-                  "in its C++17 guaranteed copy elision support. Use a newer GCC "
-                  "version, or Clang 6 or later by passing \"use_llvm=yes\" to the "
-                  "SCons command line.")
+        if major == 8 and minor < 4:
+            print("Detected GCC 8 version < 8.4, which is not supported due to a "
+                  "regression in its C++17 guaranteed copy elision support. Use a "
+                  "newer GCC version, or Clang 6 or later by passing \"use_llvm=yes\" "
+                  "to the SCons command line.")
             sys.exit(255)
         elif major < 7:
             print("Detected GCC version older than 7, which does not fully support "
                   "C++17. Supported versions are GCC 7, 9 and later. Use a newer GCC "
                   "version, or Clang 6 or later by passing \"use_llvm=yes\" to the "
                   "SCons command line.")
             sys.exit(255)
-    elif methods.using_clang(env):
+    elif version is not None and methods.using_clang(env):
+        major = int(version[0])
         # Apple LLVM versions differ from upstream LLVM version \o/, compare
         # in https://en.wikipedia.org/wiki/Xcode#Toolchain_versions
         if env["platform"] == "osx" or env["platform"] == "iphone":

methods.py

@@ -557,14 +557,18 @@ def is_vanilla_clang(env):
 
 
 def get_compiler_version(env):
+    """
+    Returns an array of version numbers as strings: [major, minor, patch].
+    The return array should have at least two values (major, minor).
+    """
     if using_gcc(env):
         version = decode_utf8(subprocess.check_output([env['CXX'], '-dumpversion']).strip())
     elif using_clang(env):
         # Not using -dumpversion as it used to return 4.2.1: https://reviews.llvm.org/D56803
         version = decode_utf8(subprocess.check_output([env['CXX'], '--version']).strip())
     else:  # TODO: Implement for MSVC
         return None
-    match = re.search('[0-9][0-9.]*', version)
+    match = re.search('[0-9]+\.[0-9.]*', version)
     if match is not None:
         return match.group().split('.')
     else: