[BOLT] Force frame pointers off for runtimes

Distributions are making the choice to turn frame pointers on by
default. Nixpkgs recently turned them on, and the method they use to do
so implies that everything is built with them on by default.

NixOS/nixpkgs#399014

Assuming that a well behaved distribution doing this puts
'-fno-omit-frame-pointer' at the beginning of the compiler invocation,
we can still re-enable it by supplying -fomit-frame-pointer thereafter.

See also: #147569

Author: peterwaller-arm

bolt/runtime/CMakeLists.txt

@@ -35,7 +35,10 @@ set(BOLT_RT_FLAGS
   -fno-exceptions
   -fno-rtti
   -fno-stack-protector
-  -fPIC)
+  -fPIC
+  -mgeneral-regs-only
+  -fomit-frame-pointer # Runtime currently assumes omitted frame pointers. llvm/llvm-project#147569
+)
 if (CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64")
   set(BOLT_RT_FLAGS ${BOLT_RT_FLAGS} 
     -mno-sse