Merge bitcoin#29756: doc: Override -g properly to skip debugging information

f8f5cec doc: Override `-g` properly to skip debugging information (Hennadii Stepanov)

Pull request description:

  Fix bitcoin#29755.

ACKs for top commit:
  TheCharlatan:
    ACK f8f5cec

Tree-SHA512: 02bff5fc41859deb914531ef01ea1ac88ab2e138219fe175472962192b11feefe772128da03f466ec765c1b35b21eead31a42cc76e62ecb7ea5dc947cf568d61

Author: fanquake

doc/build-unix.md

@@ -30,7 +30,7 @@ tuned to conserve memory with additional CXXFLAGS:
 Alternatively, or in addition, debugging information can be skipped for compilation. The default compile flags are
 `-g -O2`, and can be changed with:
 
-    ./configure CXXFLAGS="-O2"
+    ./configure CXXFLAGS="-g0"
 
 Finally, clang (often less resource hungry) can be used instead of gcc, which is used by default: