depends: Avoid using helper variables in toolchain file #31360

1. 
   hebasto commented at 1:49 pm on November 24, 2024: member

   Using helper variables has two issues:

   1. They contaminate the global namespace of the main build script.
   2. They can be used as set(var), effectively exposing a cache variable var, which makes the toolchain file susceptible to the build environment.

   The depends/Makefile can generate values with “not-set” semantics as empty strings or strings containing only spaces. For example:https://github.com/bitcoin/bitcoin/blob/2638fdb4f934be96b7c798dbac38ea5ab8a6374a/depends/Makefile#L157 Therefore, MATCHES must be used rather than STREQUAL.

2. depends: Avoid using helper variables in toolchain file

   Using helper variables has two issues:
   1. They contaminate the global namespace of the main build script.
   2. They can be used as `set(var)`, effectively exposing a cache variable
   `var`, which makes the toolchain file susceptible to the build
   environment.

   1e7cdb04fd
3. 
   DrahtBot commented at 1:50 pm on November 24, 2024: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/31360.

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4. DrahtBot added the label Build system on Nov 24, 2024

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