runtime,cmd/compile: `SIGILL` on linux/riscv64

[gopherbot]

#!watchflakes
post <- goos == "linux" && goarch == "riscv64" && log ~ `SIGILL: illegal instruction` && date < "2023-08-25"

Issue created automatically to collect these failures.

Example (log):

SIGILL: illegal instruction
PC=0x466a0 m=3 sigcode=1
instruction bytes: 0xe7 0x80 0x2 0x0 0x13 0x5 0x1 0x2 0xef 0x0 0x0 0x77 0x93 0xf2 0xf5 0xf

ra  0x466ac	sp  0x3f8b8ea210
gp  0x49e1e0	tp  0x3feb1403e0
t0  0x1f2a80	t1  0x3f8b8ea478
t2  0x0	s0  0x0
s1  0x3f8b8ea4a0	a0  0x3f8b8eaab0
a1  0x1	a2  0x3f8b8ea298
...
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/proc.go:398 +0x10c fp=0x3f880365e8 sp=0x3f880365d0 pc=0x4a3dc
runtime.chanrecv(0x3f88054380, 0x3f880366cf, 0x24?)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/chan.go:583 +0x430 fp=0x3f88036660 sp=0x3f880365e8 pc=0x15258
runtime.chanrecv1(0x52f8a0?, 0x29dca0?)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/chan.go:442 +0x14 fp=0x3f88036680 sp=0x3f88036660 pc=0x14e0c
testing.(*T).Run(0x3f880c21a0, {0x2f9669?, 0x2e742660fb676?}, 0x3f8800b1e8)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/testing/testing.go:1649 +0x380 fp=0x3f88036738 sp=0x3f88036680 pc=0xf7a38
golang.org/x/tools/gopls/internal/lsp/analysis/unusedvariable_test.Test(0x0?)
	/tmp/workdir-host-linux-riscv64-unmatched/gopath/src/golang.org/x/tools/gopls/internal/lsp/analysis/unusedvariable/unusedvariable_test.go:21 +0xf8 fp=0x3f88036778 sp=0x3f88036738 pc=0x2705b0
testing.tRunner(0x3f880c21a0, 0x311078)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/tools/gopls/internal/lsp/analysis/unusedvariable" && test == "Test"

2023-08-07 19:27 linux-riscv64-unmatched tools@f42bca8e go@3393155a x/tools/gopls/internal/lsp/analysis/unusedvariable.Test (log)

SIGILL: illegal instruction
PC=0x466a0 m=3 sigcode=1
instruction bytes: 0xe7 0x80 0x2 0x0 0x13 0x5 0x1 0x2 0xef 0x0 0x0 0x77 0x93 0xf2 0xf5 0xf

ra  0x466ac	sp  0x3f8b8ea210
gp  0x49e1e0	tp  0x3feb1403e0
t0  0x1f2a80	t1  0x3f8b8ea478
t2  0x0	s0  0x0
s1  0x3f8b8ea4a0	a0  0x3f8b8eaab0
a1  0x1	a2  0x3f8b8ea298
...
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/proc.go:398 +0x10c fp=0x3f880365e8 sp=0x3f880365d0 pc=0x4a3dc
runtime.chanrecv(0x3f88054380, 0x3f880366cf, 0x24?)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/chan.go:583 +0x430 fp=0x3f88036660 sp=0x3f880365e8 pc=0x15258
runtime.chanrecv1(0x52f8a0?, 0x29dca0?)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/runtime/chan.go:442 +0x14 fp=0x3f88036680 sp=0x3f88036660 pc=0x14e0c
testing.(*T).Run(0x3f880c21a0, {0x2f9669?, 0x2e742660fb676?}, 0x3f8800b1e8)
	/tmp/workdir-host-linux-riscv64-unmatched/go/src/testing/testing.go:1649 +0x380 fp=0x3f88036738 sp=0x3f88036680 pc=0xf7a38
golang.org/x/tools/gopls/internal/lsp/analysis/unusedvariable_test.Test(0x0?)
	/tmp/workdir-host-linux-riscv64-unmatched/gopath/src/golang.org/x/tools/gopls/internal/lsp/analysis/unusedvariable/unusedvariable_test.go:21 +0xf8 fp=0x3f88036778 sp=0x3f88036738 pc=0x2705b0
testing.tRunner(0x3f880c21a0, 0x311078)

— watchflakes