As the following testcase shows, unwind.h on ARM can't be (starting with GCC
10) compiled with -std=c* modes, only -std=gnu* modes.
The problem is it uses asm keyword, which isn't a keyword in those modes
(system headers vs. non-system ones don't make a difference here).
glibc and other installed headers use __asm or __asm__ keywords instead that
work fine in both standard and gnu modes.

While there, as it is an installed header, I think it is also wrong to
completely ignore any identifier namespace rules.
The generic unwind.h defines just _Unwind* namespace identifiers plus
_sleb128_t/_uleb128_t (but e.g. unlike libstdc++/glibc headers doesn't
uglify operand names), the ARM unwind.h is much worse here.  I've just
changed the gnu_Unwind_Find_got function at least not be in user identifier
namespace, but perhaps it would be good to go further and rename e.g.
or e.g.
  typedef _Unwind_Reason_Code (*personality_routine) (_Unwind_State,
      _Unwind_Control_Block *, _Unwind_Context *);
in unwind-arm-common.h.

2020-02-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/93615
	* config/arm/unwind-arm.h (gnu_Unwind_Find_got): Rename to ...
	(_Unwind_gnu_Find_got): ... this.  Use __asm instead of asm.  Remove
	trailing :s in asm.  Formatting fixes.
	(_Unwind_decode_typeinfo_ptr): Adjust caller.

	* gcc.dg/pr93615.c: New test.