BuildError when using multiline string in package.py

[bpabel]

The following package.py will throw a BuildError when running rez-build

name = "fakepack"
version = "1.0.0"
description = """
This is a fake package.
Some more text.
And more text.
"""
build_command = ""

Output:

$ rez-build

================================================================================
Building fakepack-1.0.0...
================================================================================
Resolving build environment:
resolved by X@X, on Tue Oct 06 14:52:27 2020, using Rez v2.62.0

requested packages:
~platform==windows         (implicit)
~arch==AMD64               (implicit)
~os==windows-6.1.7601.SP1  (implicit)

resolved packages:

Invoking custom build system...
Running build command:
'Some' is not recognized as an internal or external command,
operable program or batch file.
'And' is not recognized as an internal or external command,
operable program or batch file.
14:52:27 ERROR    BuildError: The custom build system failed.

[JeanChristopheMorinPerso]

#417