Investigate build instability LLBuildProgressTracker crashes

[ktoso]

On CI we frequently get crashes like this:

Thread 4 crashed:

0                         0x00007f1559da359a swift_slowAlloc + 74 in [libswiftCore.so](http://libswiftcore.so/)
1 [ra]                    0x00007f1559da3877 swift_allocObject + 38 in [libswiftCore.so](http://libswiftcore.so/)
2 [ra]                    0x00007f1559b85571 _allocateStringStorage(codeUnitCapacity:) + 160 in [libswiftCore.so](http://libswiftcore.so/)
3 [ra]                    0x00007f1559d03452 _StringGuts.grow(_:) + 273 in [libswiftCore.so](http://libswiftcore.so/)
4 [ra]                    0x00007f1559bf7e88 specialized static String._fromUTF8Repairing(_:) + 999 in [libswiftCore.so](http://libswiftcore.so/)
5 [ra] [inlined] [system] 0x000056315a96e7ef specialized String.init<A, B>(decoding:as:) in swift-package at //<compiler-generated>
6 [ra] [inlined]          0x000056315a96e7ef stringFromData(_:) in swift-package at /home/build-user/llbuild/products/llbuildSwift/Internals.swift:49:12
7 [ra]                    0x000056315a96e7ef Command.name.getter + 78 in swift-package at /home/build-user/llbuild/products/llbuildSwift/BuildSystemBindings.swift:720:20
8 [ra]                    0x00005631593a61a2 closure #1 in LLBuildProgressTracker.commandProcessFinished(_:process:result:) + 33 in swift-package at /home/build-user/swiftpm/Sources/Build/LLBuildProgressTracker.swift:347:65
9 [ra] [thunk]            0x00005631592f6989 thunk for @escaping @callee_guaranteed @Sendable () -> () + 24 in swift-package at //<compiler-generated>

Rebuilding usually gets rid of the issue... We need to figure out what's going on here. I've already reached out to swiftpm team also for any ideas.

rdar://155752697