[5.5] Enable checking for -no-toolchain-stdlib-rpath and use it on this repo's binaries before installing

[finagolfin]

Cherry-pick of #732 and #767

• Explanation: This matches the upstream driver and removes the build toolchain's rpath for this shipping swift-driver executable itself on ELF platforms.
• Scope: Adds behavior to match upstream and remove an extraneous rpath from the swift-driver and other executables from this repo.
• Risk: None
• Testing: Passes all tests, as indicated in the upstream pull, and should now pass more tests from the compiler test suite.
• Reviewer: @artemcm

[finagolfin]

@varungandhi-apple, would you run the CI on this?

[artemcm]

@swift-ci please test

[finagolfin]

Passed CI, ready to merge.

[finagolfin]

@DougGregor, would be good to get this in as it fixes a security issue on linux. The latest official prebuilt Swift 5.5 snapshot toolchains use swift-driver by default, which has this ELF RPATH:

> readelf -d swift-5.5-DEVELOPMENT-SNAPSHOT-2021-07-03-a-centos8/usr/bin/swift-driver | ag runpath
0x000000000000001d (RUNPATH)            Library runpath: [/home/build-user/swift-nightly-install/usr/lib/swift/linux:$ORIGIN:$ORIGIN/../lib/swift/linux]

This pull will remove that first /home/build-user/ path.

[finagolfin]

Ping, would be good to get this in.

[finagolfin]

@artemcm, anything holding this up?

[artemcm]

@buttaface, we will try and get this in; but, before we do, could you please add an XCTest for this change and then include it in the cherry-pick? Despite the compiler's validation suite, we would still like to have the driver's own test-suite capture these things in XCTests to be more stand-alone w.r.t. the compiler.
I apologize, I really should have pointed that out on the original review.

[finagolfin]

No problem, submitted for trunk in #767, will cherry-pick here once it's in.

[finagolfin]

Cherry-picked the test too.

[finagolfin]

Anything holding this up? I think it just needs to be run on the CI with the new test and then we can get it in.

[artemcm]

@swift-ci please test