clang-format: set SpaceBeforeParens to ControlStatementsExceptForEachMacros

I contributed this option to LLVM a while ago to reduce the amount of
changes clang-format makes when formatting systemd source files. As
LLVM 11 is now starting to becomes widely available, let's configure
it in the clang-format config.

.clang-format

@@ -118,6 +118,7 @@ PenaltyBreakString: 0
 PenaltyExcessCharacter: 10
 PenaltyReturnTypeOnItsOwnLine: 100
 SpaceAfterCStyleCast: true
+SpaceBeforeParens: ControlStatementsExceptForEachMacros
 SpacesInAngles:  true
 TabWidth:        8
 UseCRLF:         false