[dev.typeparams] all: merge master (785a8f67) into dev.typeparams

- test/run.go

  CL 328050 added fixedbugs/issue46749.go to -G=3 excluded files list

Merge List:

+ 2021-06-16 785a8f67 cmd/compile: better error message for invalid untyped operation
+ 2021-06-16 a752bc07 syscall: fix TestGroupCleanupUserNamespace test failure on Fedora
+ 2021-06-15 d77f4c0c net/http: improve some server docs
+ 2021-06-15 219fe9d5 cmd/go: ignore UTF8 BOM when reading source code
+ 2021-06-15 723f199e cmd/link: set correct flags in .dynamic for PIE buildmode
+ 2021-06-15 4d2d89ff cmd/go, go/build: update docs to use //go:build syntax
+ 2021-06-15 033d8853 doc/go1.17: document go run pkg@version
+ 2021-06-15 ea8612ef syscall: disable c-shared test when no cgo, for windows/arm
+ 2021-06-15 abc56fd1 internal/bytealg: remove duplicate go:build line
+ 2021-06-15 4061d346 syscall: rewrite handle inheritance test to use C rather than Powershell
+ 2021-06-15 cf4e3e3d reflect: explain why convertible or comparable types may still panic
+ 2021-06-14 7841cb14 doc/go1.17: assorted fixes
+ 2021-06-14 8a5a6f46 debug/elf: don't apply DWARF relocations for ET_EXEC binaries
+ 2021-06-14 9d13f8d4 runtime: update the variable name in comment
+ 2021-06-14 0fd20ed5 reflect: use same conversion panic in reflect and runtime
+ 2021-06-14 6bbb0a9d cmd/internal/sys: mark windows/arm64 as c-shared-capable
+ 2021-06-14 d4f34f8c doc/go1.17: reword "results" in stack trace printing

Change-Id: I60d1f67c4d48cd4093c350fc89bd60c454d23944