build: fix quiet default for make builds

[codebytere]

The Makefile says builds are quiet unless V=1 (since #26740), but it sets V ?= 0 and forwards V=$(V) to the gyp-generated makefile, which checks ifdef V. 0 is a non-empty value, so every make build has printed the full compiler command lines regardless. On ci.nodejs.org that is most of the log volume: one node-test-commit-* configuration's console is 12-22 MB with all but ~0.5 MB of it compile commands before the TAP output starts, and a single node-test-pull-request run adds up to ~480 MB of console on the controller (nodejs/build#4419).

This defaults V to empty so the sub-make sees no V and uses its quiet_ rules. make V=1, or V=1 in the environment, is verbose as before; the ninja and cpplint paths already compare against 1 and are unchanged.

Tests: on a make-configured tree make now prints CC(target) … lines and make V=1 prints the full commands; make -n node shows V= / V=1 being forwarded.

Refs: #26740
Refs: nodejs/build#4419

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Disclosure: the code and this description were written by Claude Code, directed and reviewed by @codebytere.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.18%. Comparing base (b0d56c7) to head (935cb7c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65826      +/-   ##
==========================================
- Coverage   90.19%   90.18%   -0.02%     
==========================================
  Files         770      770              
  Lines      264410   264410              
  Branches    50243    50240       -3     
==========================================
- Hits       238490   238446      -44     
- Misses      16924    16978      +54     
+ Partials     8996     8986      -10     

see 32 files with indirect coverage changes

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