* Clarify stub compiler definition in compilers.yaml
* Update explanation of why stub compiler definition is needed
* Add note about required module definition when using Spack-installed
intel-parallel-studio as intel-compiler
* Add suggestion about updating package config preferences based on
choice of variants when installing intel-parallel-studio to avoid
reinstallation
on multilib distros with lib/lib64 (rather than lib32/lib) the library ends up in a dir lib64/ instead of lib/, breaking the libs property (and the cp2k+spglib build)
We remove system paths from search variables like PATH and
from -L options because they may contain many packages and
could interfere with Spack-built packages. External packages
may be installed to prefixes that are not actually system paths
but are still "merged" in the sense that many other packages are
installed there. To avoid conflicts, this PR places all external
packages at the end of search paths.
See #17270.
```
make[2]: Entering directory `/tmp/vavolkl/spack-stage/spack-stage-qt-5.14.2-63dapppjbq6vqh3le7pazsprijls7cfl/spack-src/qtwebengine/src'
/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `echo Modules will not be built. Python version 2 (2.7.5 or later) is required to build QtWebEngine.'
make[2]: *** [errorbuild] Error 1
```
We set LC_ALL=C to encourage a build process to generate ASCII
output (so our logger daemon can decode it). Most packages
respect this but it appears that intel-oneapi-compilers does
not in some cases (see #22813). This reads the output of the build
process as UTF-8, which still works if the build process respects
LC_ALL=C but also works if the process generates UTF-8 output.
For Python >= 3.7 all files are opened with UTF-8 encoding by
default. Python 2 does not support the encoding argument on
'open', so to support Python 2 the files would have to be
opened in byte mode and explicitly decoded (as a side note,
this would be the only way to handle other encodings without
being informed of them in advance).
