clang-format: Add file

Related: orage#32, xfce/xfce4-dev-tools!101

.clang-format

+---
+Language: Cpp
+BasedOnStyle: LLVM
+
+AlignEscapedNewlines: DontAlign
+AlignTrailingComments: Never
+AllowAllParametersOfDeclarationOnNextLine: false
+AlwaysBreakAfterReturnType: All
+BreakBeforeBinaryOperators: NonAssignment
+ColumnLimit: 0
+Cpp11BracedListStyle: false
+IncludeBlocks: Regroup
+IncludeCategories:
+  - Regex: '"config\.h"'
+    Priority: -3
+    CaseSensitive: true
+  - Regex: '<.*>'
+    Priority: -2
+    CaseSensitive: true
+  - Regex: '".*/.*"'
+    Priority: -1
+    CaseSensitive: true
+  - Regex: '"[^/]*"'
+    Priority: 0
+    SortPriority: 1
+    CaseSensitive: true
+IndentCaseLabels: true
+IndentWidth: 4
+InsertNewlineAtEOF: true
+MaxEmptyLinesToKeep: 3
+SpaceAfterCStyleCast: true
+SpaceBeforeParens: Always
+WhitespaceSensitiveMacros:
+  # Buggy workaround to add exceptions to 'SpaceBeforeParens: Always' (see below)
+  - _
+# Workaround to avoid some alignment bugs when adding a macro to WhitespaceSensitiveMacros,
+# see https://github.com/llvm/llvm-project/issues/55443#issuecomment-1953268337
+# This doesn't fix all alignment bugs though, so I'd rather make an exception only for '_',
+# and not also for 'N_' or 'I_' for example.
+# See also https://github.com/llvm/llvm-project/issues/82288
+Macros:
+  - _(x)=x
+...