GCC's x86 and s390 ports support -mrecord-mcount. Other ports reject the
option.
aarch64-linux-gnu-gcc: error: unrecognized command line option ‘-mrecord-mcount’
Allowing this option can cause failures when building Linux kernel for
aarch64, powerpc64, etc, which will think the feature is available if
the clang command returns 0.
Let the "mnop-mcount" function attribute simply be present or non-present.
Update SystemZ backend as well to use hasFnAttribute() instead.
Review: Ulrich Weigand
https://reviews.llvm.org/D71669
Recognize -mnop-mcount from the command line and add a function attribute
"mnop-mcount"="true" when passed.
When this option is used, a nop is added instead of a call to fentry. This
is used when building the Linux Kernel.
If this option is passed for any other target than SystemZ, an error is
generated.
Review: Ulrich Weigand
https://reviews.llvm.org/D67763
Fangrui Song