newLib fails to build with shellcmd cmd failed error

Summary

I am trying to build newLib with rtems source builder in cygwin64 and Linux, but in both situations the build fails. I use the rtems-gcc-13.3-newlib-head.cfg file and I get the error:

Makefile:1040: recipe for target 'all' failed 
make: \*\*\* \[all\] Error 2 make: Leaving directory '/home/jenkins/agent/workspace/\_RiscV_Tools_Update-to-gcc-to-13/riscvtools/rtems/build/riscv-rtems6-gcc-13.3.0-newlib-1ed1516-x86_64-linux-gnu-1/build' 
shell cmd failed: /bin/sh -ex /home/jenkins/agent/workspace/\_RiscV_Tools_Update-to-gcc-to-13/riscvtools/rtems/build/riscv-rtems6-gcc-13.3.0-newlib-1ed1516-x86_64-linux-gnu-1/do-build 
error: building riscv-rtems6-gcc-13.3.0-newlib-1ed1516-x86_64-linux-gnu-1
See error report: rsb-report-riscv-rtems6-gcc-13.3.0-newlib-1ed1516-x86_64-linux-gnu-1.txt 
Note: In some cases the error appears only in the complete build log (see --log option)

I've noticed in the Makefile created there is an extra '+' character. The previous Makefile was created after rtems-gcc-9.3.0-newlib-7947581.cfg and doesn't have that '+' character.

Steps to reproduce