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/[e-mail]/T/#u
[2] https://lore.kernel.org/lkml/20181218140105.ajuiglkpvstt3qxs@treble/T/#u
[3] https://patchwork.kernel.org/patch/8707981/#21817015

This reverts commit 95272c29378ee7dc15f43fa2758cb28a5913a06d.

Suggested-by: Andi Kleen <[e-mail]>
Cc: Paolo Bonzini <[e-mail]>
Cc: Nadav Amit <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Cc: Martin Jambor <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Miroslav Benes <[e-mail]>
Signed-off-by: Sean Christopherson <[e-mail]>
Reviewed-by: Andi Kleen <[e-mail]>
Reviewed-by: Miguel Ojeda <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

include/linux/compiler_attributes.h

···
 # 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
···
 
 /*
  * 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