[libc++] Set CMAKE_FOLDER. NFC.

* This variable populates the default value of FOLDER target property. It is used in some IDE's (e.g. MSVC) to group different targets together.

GitOrigin-RevId: 5e7a93a954e68b002edd2cd7fb1b2a61186c7124
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ede8bd7..b803347 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,6 +17,8 @@
   ${CMAKE_MODULE_PATH}
   )
 
+set(CMAKE_FOLDER "libc++")
+
 set(LIBCXXABI_SOURCE_DIR  ${CMAKE_CURRENT_SOURCE_DIR})
 set(LIBCXXABI_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
 set(LIBCXXABI_LIBCXX_PATH "${CMAKE_CURRENT_LIST_DIR}/../libcxx" CACHE PATH