[libcxx][NFC] adjusts formatting rules

This will reduce the amount of noisy feedback during reviews.

Differential Revision: https://reviews.llvm.org/D99691

libcxx/.clang-format

@@ -10,4 +10,11 @@ PointerAlignment: Left
 # Disable formatting options which may break tests.
 SortIncludes: false
 ReflowComments: false
+
+# libc++ has some long names so we need more than the 80 column limit imposed by LLVM style, for sensible formatting
+ColumnLimit: 120
+
+# These aren't covered by the LLVM Style Guide
+BreakBeforeConceptDeclarations: true
+IndentRequires: false
 ---