[libcxx] [docs] Remove mention of a MSVC/Debug mode caveat (#68791)

Since e346fd8 and
cd1b8be, the tests should run fine in
Debug mode, with failed asserts not popping up blocking dialog boxes.

Author: mstorsjo

libcxx/docs/BuildingLibcxx.rst

@@ -145,9 +145,6 @@ should add e.g. ``-DCMAKE_CXX_COMPILER_TARGET=x86_64-windows-msvc`` (replacing
 line above. This will instruct ``check-cxx`` to use the right target triple
 when invoking ``clang++``.
 
-Also note that if not building in Release mode, a failed assert in the tests
-pops up a blocking dialog box, making it hard to run a larger number of tests.
-
 CMake + ninja (MinGW)
 ---------------------