add support for shared_ptr casts

Note that this commit also introduces a new config variable, cpp_no_cpp17.

Author: Smattr

syntax/cpp.vim

@@ -41,6 +41,8 @@ if !exists("cpp_no_cpp11")
   syn keyword cppConstant	ATOMIC_INT_LOCK_FREE ATOMIC_LONG_LOCK_FREE
   syn keyword cppConstant	ATOMIC_LLONG_LOCK_FREE ATOMIC_POINTER_LOCK_FREE
   syn region cppRawString	matchgroup=cppRawStringDelimiter start=+\%(u8\|[uLU]\)\=R"\z([[:alnum:]_{}[\]#<>%:;.?*\+\-/\^&|~!=,"']\{,16}\)(+ end=+)\z1"+ contains=@Spell
+  syn match cppCast		"\<\(const\|static\|dynamic\)_pointer_cast\s*<"me=e-1
+  syn match cppCast		"\<\(const\|static\|dynamic\)_pointer_cast\s*$"
 endif
 
 " C++ 14 extensions
@@ -52,6 +54,12 @@ if !exists("cpp_no_cpp14")
   syn case match
 endif
 
+" C++ 17 extensions
+if !exists("cpp_no_cpp17")
+  syn match cppCast		"\<reinterpret_pointer_cast\s*<"me=e-1
+  syn match cppCast		"\<reinterpret_pointer_cast\s*$"
+endif
+
 " The minimum and maximum operators in GNU C++
 syn match cppMinMax "[<>]?"