Add a .clang-format file

It gets hard to code in GNU style for people with editors that don't
understand the difference between indentwidth and tabstop.

This file is based on gcc's contrib/clang-format. A flaw of it is that
it does not put a space after selector colons. I am gonna file a LLVM
bug for that.

.clang-format

@@ -0,0 +1,77 @@
+# Copyright (C) 2015 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Modified from gcc's clang-format config.
+
+# clang-format 7.0.1 is required
+#
+# To utilize the tool to lines just touched by a patch, use
+# clang-format-diff script that is usually also packaged with clang-format.
+#
+# Example of usage:
+# git diff -U0 --no-color | clang-format-diff -p1
+# (here the tool will generate a patch)
+# git diff -U0 --no-color | clang-format-diff -p1 -i
+# (modifications are applied)
+
+---
+AccessModifierOffset: -2
+AlwaysBreakAfterReturnType: TopLevel
+AlignConsecutiveDeclarations: true
+BinPackArguments: true
+BinPackParameters: true
+BreakBeforeBinaryOperators: All
+BreakBeforeBraces: Custom
+# Newer clang-format has BS_GNU
+BraceWrapping:
+  AfterClass: true
+  AfterControlStatement: true
+  AfterEnum: true
+  AfterFunction: true
+  AfterNamespace: false
+  AfterObjCDeclaration: true
+  AfterStruct: true
+  AfterUnion: true
+  BeforeCatch: true
+  BeforeElse: true
+  IndentBraces: true
+  SplitEmptyFunction: false
+BreakBeforeTernaryOperators: true
+ColumnLimit: 80
+ConstructorInitializerIndentWidth: 2
+ContinuationIndentWidth: 2
+ObjCBlockIndentWidth: 2
+ObjCSpaceAfterProperty: true
+ObjCSpaceBeforeProtocolList: true
+ForEachMacros: []
+IndentCaseLabels: false
+NamespaceIndentation: None
+PenaltyBreakBeforeFirstCallParameter: 100
+DerivePointerAlignment: false
+PointerAlignment: Right
+SortIncludes: false
+SpaceAfterCStyleCast: true
+SpaceBeforeParens: ControlStatements
+SpacesBeforeTrailingComments: 1
+UseTab: Always
+AlignEscapedNewlines: Right
+AlignTrailingComments: true
+AllowShortFunctionsOnASingleLine: All
+AlwaysBreakTemplateDeclarations: MultiLine
+KeepEmptyLinesAtTheStartOfBlocks: false
+
+# TODO
+# MacroBlockBegin: 
+# MacroBlockEnd: