boost: Allow apple-clang version 10 for nowide and C++ 11

- Tested with apple-clang 10.0, which is equivalent to clang 4.2.

- Boost config reports that std::fstream is swappable and movable.

recipes/boost/all/conanfile.py

@@ -137,7 +137,7 @@ def _min_compiler_version_default_cxx11(self):
         return {
             "gcc": 6,
             "clang": 6,
-            "apple-clang": 12,  # guess
+            "apple-clang": 10,
             "Visual Studio": 14,  # guess
         }.get(str(self.settings.compiler))
 
@@ -147,7 +147,7 @@ def _min_compiler_version_nowide(self):
         return {
             "gcc": 5,
             "clang": 5,
-            "apple-clang": 12,  # guess
+            "apple-clang": 10,
             "Visual Studio": 14,  # guess
         }.get(str(self.settings.compiler))