Rollup of 10 pull requests

[Manishearth]

Successful merges:

• Properly encode AnonConst into crate metadata #72600 (Properly encode AnonConst into crate metadata)
• RISC-V Emulated Testing #73171 (RISC-V Emulated Testing)
• Remove use of specialization from librustc_arena #73378 (Remove use of specialization from librustc_arena)
• Update CFGuard syntax #73404 (Update CFGuard syntax)
• Update bootstrap to rustc 1.45.0-beta.2 (1dc0f6d8e 2020-06-15) #73411 (Update bootstrap to rustc 1.45.0-beta.2 (1dc0f6d 2020-06-15))
• Update cargo #73415 (Update cargo)
• ci: allow gating GHA on everything but macOS #73443 (ci: allow gating GHA on everything but macOS)
• ci: disable alt build during try builds #73444 (ci: disable alt build during try builds)
• Prevent attacker from manipulating FPU tag word used in SGX enclave #73471 (Prevent attacker from manipulating FPU tag word used in SGX enclave)
• Converted all platform-specific stdin/stdout/stderr implementations to use io:: traits #73495 (Converted all platform-specific stdin/stdout/stderr implementations to use io:: traits)

Failed merges:

• Projection bound validation #72788 (Projection bound validation)

r? @ghost