kcsan: Update Documentation to change supported compilers

Document change in required compiler version for KCSAN, and remove the
now redundant note about __no_kcsan and inlining problems with older
compilers.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-8-elver@google.com

Documentation/dev-tools/kcsan.rst

@@ -8,8 +8,7 @@ approach to detect races. KCSAN's primary purpose is to detect `data races`_.
 Usage
 -----
 
-KCSAN is supported in both GCC and Clang. With GCC it requires version 7.3.0 or
-later. With Clang it requires version 7.0.0 or later.
+KCSAN requires Clang version 11 or later.
 
 To enable KCSAN configure the kernel with::
 
@@ -121,12 +120,6 @@ the below options are available:
     static __no_kcsan_or_inline void foo(void) {
         ...
 
-  Note: Older compiler versions (GCC < 9) also do not always honor the
-  ``__no_kcsan`` attribute on regular ``inline`` functions. If false positives
-  with these compilers cannot be tolerated, for small functions where
-  ``__always_inline`` would be appropriate, ``__no_kcsan_or_inline`` should be
-  preferred instead.
-
 * To disable data race detection for a particular compilation unit, add to the
   ``Makefile``::