This patch implemented TTI.IntImmCost() properly.
Each BPF insn has 32bit immediate space, so for any immediate
which can be represented as 32bit signed int, the cost
is technically free. If an int cannot be presented as
a 32bit signed int, a ld_imm64 instruction is needed
and a TCC_Basic is returned.

This change is motivated when we observed that
several bpf selftests failed with latest llvm trunk, e.g.,
  #10/16 strobemeta.o:FAIL
  #10/17 strobemeta_nounroll1.o:FAIL
  #10/18 strobemeta_nounroll2.o:FAIL
  #10/19 strobemeta_subprogs.o:FAIL
  #96 snprintf_btf:FAIL

The reason of the failure is due to that
SpeculateAroundPHIsPass did aggressive transformation
which alters control flow for which currently verifer
cannot handle well. In llvm12, SpeculateAroundPHIsPass
is not called.

SpeculateAroundPHIsPass relied on TTI.getIntImmCost()
and TTI.getIntImmCostInst() for profitability
analysis. This patch implemented TTI.getIntImmCost()
properly for BPF backend which also prevented
transformation which caused the above test failures.

Differential Revision: https://reviews.llvm.org/D96448

This patch implemented TTI.IntImmCost() properly.
Each BPF insn has 32bit immediate space, so for any immediate
which can be represented as 32bit signed int, the cost
is technically free. If an int cannot be presented as
a 32bit signed int, a ld_imm64 instruction is needed
and a TCC_Basic is returned.

This change is motivated when we observed that
several bpf selftests failed with latest llvm trunk, e.g.,
  #10/16 strobemeta.o:FAIL
  #10/17 strobemeta_nounroll1.o:FAIL
  #10/18 strobemeta_nounroll2.o:FAIL
  #10/19 strobemeta_subprogs.o:FAIL
  #96 snprintf_btf:FAIL

The reason of the failure is due to that
SpeculateAroundPHIsPass did aggressive transformation
which alters control flow for which currently verifer
cannot handle well. In llvm12, SpeculateAroundPHIsPass
is not called.

SpeculateAroundPHIsPass relied on TTI.getIntImmCost()
and TTI.getIntImmCostInst() for profitability
analysis. This patch implemented TTI.getIntImmCost()
properly for BPF backend which also prevented
transformation which caused the above test failures.

Differential Revision: https://reviews.llvm.org/D96448

(cherry picked from commit a260ae7)

This PR adds support for thread names in lldb on Windows.

```
(lldb) thr list
Process 2960 stopped
  thread #53: tid = 0x03a0, 0x00007ff84582db34 ntdll.dll`NtWaitForMultipleObjects + 20
  thread #29: tid = 0x04ec, 0x00007ff845830a14 ntdll.dll`NtWaitForAlertByThreadId + 20, name = 'SPUW.6'
  thread #89: tid = 0x057c, 0x00007ff845830a14 ntdll.dll`NtWaitForAlertByThreadId + 20, name = 'PPU[0x1000019] physics[main]'
  thread #3: tid = 0x0648, 0x00007ff843c2cafe combase.dll`InternalDoATClassCreate + 39518
  thread #93: tid = 0x0688, 0x00007ff845830a14 ntdll.dll`NtWaitForAlertByThreadId + 20, name = 'PPU[0x100501d] uMovie::StreamingThread'
  thread #1: tid = 0x087c, 0x00007ff842e7a104 win32u.dll`NtUserMsgWaitForMultipleObjectsEx + 20
  thread #96: tid = 0x0890, 0x00007ff845830a14 ntdll.dll`NtWaitForAlertByThreadId + 20, name = 'PPU[0x1002020] HLE Video Decoder'
<...>
```

… >= 4G (llvm#151460)"

This reverts commit 600976f.

The test was crashing trying to access any element of the GPR struct.

(gdb) disas
Dump of assembler code for function _ZN7testing8internal11CmpHelperEQIyyEENS_15AssertionResultEPKcS4_RKT_RKT0_:
   0x00450afc <+0>:	push	{r4, r5, r6, r7, r8, r9, r10, r11, lr}
   0x00450b00 <+4>:	sub	sp, sp, #60	; 0x3c
   0x00450b04 <+8>:	ldr	r5, [sp, #96]	; 0x60
=> 0x00450b08 <+12>:	ldm	r3, {r4, r7}
   0x00450b0c <+16>:	ldm	r5, {r6, r9}
   0x00450b10 <+20>:	eor	r7, r7, r9
   0x00450b14 <+24>:	eor	r6, r4, r6
   0x00450b18 <+28>:	orrs	r7, r6, r7

(gdb) p/x r3
$3 = 0x3e300f6e

"However, load and store multiple instructions (LDM and STM) and load and store double-word (LDRD or STRD) must be aligned to at least a word boundary."

https://developer.arm.com/documentation/den0013/d/Porting/Alignment

>>> 0x3e300f6e % 4
2

Program received signal SIGBUS, Bus error.
0x00450b08 in testing::AssertionResult testing::internal::CmpHelperEQ<unsigned long long, unsigned long long>(char const*, char const*, unsigned long long const&, unsigned long long const&) ()

The struct is packed with 1 byte alignment, but it needs to start at an aligned address for us
to ldm from it. So I've done that with alignas.

Also fixed some compiler warnings in the test itself.