#2880: backport ExternalLibraries changes for gcc-15, and RPM-based repos to Kruskal

Comment (by Roland Haas):

Backported as git hash c45b71f "ADIOS2: make compile with gcc15 by adding stdint" of ExternalLibraries-ADIOS2

Backported as git hash 0bf0d5b "Silo: force libdir when building from source" of ExternalLibraries-Silo

Backported as git hash 5bde5bf "HDF5: use env variable for --keep-system-libs instead of option" of ExternalLibraries-HDF5

Backported as git hash dcbde10 "NSIMD: update version requirements to support CMake 4.0" of ExternalLibraries-NSIMD

Backported as git hash c6ac85d "openPMD: bump version to 0.16.1" of ExternalLibraries-openPMD