Fixing the Esp32 firmware build error on Debian and Raspberry

[serg3295]

Fixes #3674 .

• This PR is for the dev branch rather than for the release branch.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/*.

To calculate BUILDINFO_LFS_SIZE, awk "{print strtonum( $1 )}" is currently used.
The strtonum() function is a gawk extension.
But the gawk package is not included by default in Debian stable.
To ensure the firmware build on all systems, we have to replace awk "{print strtonum( $1 )}" with xargs printf "%d"