Revert "compiler-gcc: disable -ftracer for __noclone functions"

The -ftracer optimization was disabled in __noclone as a workaround to
GCC duplicating a blob of inline assembly that happened to define a
global variable.  It has been pointed out that no amount of workarounds
can guarantee the compiler won't duplicate inline assembly[1], and that
disabling the -ftracer optimization has several unintended and nasty
side effects[2][3].

Now that the offending KVM code which required the workaround has
been properly fixed and no longer uses __noclone, remove the -ftracer
optimization tweak from __noclone.

[1] https://lore.kernel.org/lkml/ri6y38lo23g.fsf@suse.cz/T/#u
[2] https://lore.kernel.org/lkml/20181218140105.ajuiglkpvstt3qxs@treble/T/#u
[3] https://patchwork.kernel.org/patch/8707981/#21817015

This reverts commit 95272c2937.

Suggested-by: Andi Kleen <ak@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Martin Jambor <mjambor@suse.cz>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/compiler_attributes.h

@@ -37,7 +37,6 @@
 # define __GCC4_has_attribute___designated_init__     0
 # define __GCC4_has_attribute___externally_visible__  1
 # define __GCC4_has_attribute___noclone__             1
-# define __GCC4_has_attribute___optimize__            1
 # define __GCC4_has_attribute___nonstring__           0
 # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
 #endif
@@ -163,17 +162,11 @@
 
 /*
  * Optional: not supported by clang
- * Note: icc does not recognize gcc's no-tracer
  *
  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
- *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-optimize-function-attribute
  */
 #if __has_attribute(__noclone__)
-# if __has_attribute(__optimize__)
-#  define __noclone                     __attribute__((__noclone__, __optimize__("no-tracer")))
-# else
-#  define __noclone                     __attribute__((__noclone__))
-# endif
+# define __noclone                      __attribute__((__noclone__))
 #else
 # define __noclone
 #endif