[release/6.0-rc2] Big-endian fixes: PDB creation by ilasm

[github-actions]

Backport of #59422 to release/6.0-rc2

/cc @BruceForstall@uweigand

Customer Impact

Fixes s390x platform source-build using .NET 6 tools. No impact to supported .NET 6 platforms.

Testing

Regular PR testing + ilasm/ildasm round-trip pri-1 test run.

Risk

Low

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Issue Details

---

Backport of #59422 to release/6.0-rc2

/cc @BruceForstall@uweigand

Customer Impact

Testing

Risk

Author:	github-actions[bot]
Assignees:	-
Labels:	area-ILTools-coreclr
Milestone:	-

[JulieLeeMSFT]

cc @dotnet/jit-contrib PTAL PR for backporting to .NET 6 rc2.

[BruceForstall]

Interesting: Libraries Test Run checked coreclr Linux_musl arm64 Release failed with a GC assert:

https://helixre8s23ayyeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-pull-59484-merge-b97d5a2515314a99b1/System.Text.Json.Tests/1/console.04bc49ae.log?sv=2019-07-07&se=2021-10-12T17%3A46%3A30Z&sr=c&sp=rl&sig=%2FUKyGZNpi1W5xCIUx1tAlPKpX0Qui2tufwJ%2Bfe91Hqw%3D

Assert failure(PID 95 [0x0000005f], Thread: 141 [0x008d]): ptrdiff_t(GetNumSeries()) > 0
File: /__w/1/s/src/coreclr/vm/../gc/gcdesc.h Line: 178
Image: /root/helix/work/correlation/dotnet

This failed before with #39672, but @mangod9 recently closed the issue as it hadn't been seen in a while.

Will rerun the test, but is certainly not due to this PR.