fix(nanodump): make host-tool build work on macOS

[slimwang]

Problem

Building Creds-BOF on macOS fails in the nanodump Makefile:

ld: warning: -s is obsolete
ld: library 'crt0.o' not found
clang: error: linker command failed with exit code 1

and then:

x86_64-w64-mingw32-strip: scripts/restore_signature: file format not recognized

The cross-compiled BOF artifacts (mingw .o/.exe/.dll) build fine. The failures are only in the host-compiled helper tools (bin2c, restore_signature):

• On macOS gcc is Apple clang, which does not support -static (there is no crt0.o / static libc) nor the obsolete -s linker flag.
• restore_signature is then stripped with the mingw strip, which only understands Windows PE — not the native Mach-O binary.

Fix

Detect the host OS in Creds-BOF/nanodump/Makefile:

• Drop -static -s from the host gcc invocations on Darwin.
• Use the host strip (not the mingw strip) for the native restore_signature helper.

Linux behavior is unchanged (-static -s and mingw strip are kept).

[slimwang]

Closing as duplicate. This is already addressed by #139 (the more complete cross-platform fix, with CI, closes #129) and #144 (same minimal Makefile fix, opened earlier). No need for a third PR on the same lines.