boot/efi: Prefer nm to objdump

[emaste]

Summary

This gets us a step closer to building without binutils as we have an nm implementation from ELF Tool Chain.

Test Plan

• apply patch, verify buildworld passes
• add a call to a dummy undef function, verify buildworld fails

[emaste]

rework test to avoid bare !

[bdrewery]

Wait it has an issue

[bdrewery]

sh -c 'set -e; true | false && exit 2;'; echo $?
when the && fails it still exits with an error
putting it in a if line fixes that

if ${NM} ${.ALLSRC} | grep ' U'; then exit 1; fi

[bdrewery]

In D5613#119986, @bdrewery wrote:

sh -c 'set -e; true | false && exit 2;'; echo $?
when the && fails it still exits with an error
putting it in a if line fixes that

if ${NM} ${.ALLSRC} | grep ' U'; then exit 1; fi

But exit won't work in make so use false instead.

[bdrewery]

Or rework it to use || which won't default fail

[bdrewery]

In D5613#119987, @bdrewery wrote:

In D5613#119986, @bdrewery wrote:

sh -c 'set -e; true | false && exit 2;'; echo $?
when the && fails it still exits with an error
putting it in a if line fixes that

if ${NM} ${.ALLSRC} | grep ' U'; then exit 1; fi

But exit won't work in make so use false instead.

Sorry, exit is fine here. It's not as a bare command.

[emaste]

Update per @bdrewery's comment