intialize false_but_the_compiler_does_not_know_it_

Compiling/linking 82e79c6 on an older MacOs machine (like Xcode
14.3.1, the last version of 14.x series) leads to this:

    Undefined symbols for architecture x86_64:
      "_false_but_the_compiler_does_not_know_it_", referenced from:
	  _start_command in libgit.a(run-command.o)

The linker fails to pick up compiler-tricks/not-constant.o that
defines the needed false_but_the_compiler_does_not_know_it_ symbol,
which is the only thing defined in that object file, from the
libgit.a archive.

Initializing the variable explicitly to 0 works around the linker
bug; the symbol type changes from 'C' to 'S' and is picked up by the
linker.

Xcode 15 introduces a new linker, which seems to fix the bug, making
the workaround here unnecessary, and Apple requires to build with
Xcode 16 or later in order to upload to their App Store Connect
since April 24, 2025, but not everybody is expected to upgrade their
toolchain immediately.

Helped-by: Koji Nakamaru <[email protected]>
Signed-off-by: Torsten Bögershausen <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: tboegi

compiler-tricks/not-constant.c

@@ -1,2 +1,2 @@
 #include <git-compat-util.h>
-int false_but_the_compiler_does_not_know_it_;
+int false_but_the_compiler_does_not_know_it_ = 0;