Missing errno.h include

[mirelachirica]

Description

• include of errno.h header is needed for Mac OS X: unititests failing to compile otherwise
• removed usage of "endptr" from strtol() since its value is not used

Pull request type

[x ] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts

[rolfmobile99]

Thanks Mirela, I just found the same issue on a MacOS build of "riscv-isa-sim", a RISC-V simulator!
Found your fix after a lot of googling.
So simple.