vim: comment out #if false

Similar to `#if 0` in C/C++, `#if false` is used to block comment out code.
Treat it as such.

Author: compnerd

utils/vim/syntax/swift.vim

@@ -62,6 +62,7 @@ syn match swiftChar /'\([^'\\]\|\\\(["'tnr0\\]\|x[0-9a-fA-F]\{2}\|u[0-9a-fA-F]\{
 syn keyword swiftLabel get set
 
 syn match swiftPreproc /^\s*#\(\<if\>\|\<else\>\|\<elseif\>\|\<endif\>\)/
+syn region swiftPreprocFalse start="^\s*#\<if\>\s\+\<false\>" end="^\s*#\(\<else\>\|\<elseif\>\|\<endif\>\)"
 
 syn match swiftAttribute /@\<\w\+\>/ skipwhite
 
@@ -103,6 +104,7 @@ hi def link swiftLabel Operator
 hi def link swiftNew Operator
 hi def link swiftMutating Statement
 hi def link swiftPreproc PreCondit
+hi def link swiftPreprocFalse Comment
 hi def link swiftAttribute Type
 hi def link swiftTodo Todo
 hi def link swiftNil Constant