Add static linking support for Codon runtime

This PR introduces static linking capabilities for the Codon runtime library, addressing the need for self-contained executables without external runtime dependencies.

Changes:

• Added codonrt_static target that builds a static version of the runtime library
• Created codonrt_static_combined target that combines all dependencies into a single static library
• Modified writeToExecutable() to prefer static linking when libcodonrt_static_combined.a is available
• Added platform-specific handling for combining static libraries (libtool on macOS, ar on Linux)
• Updated install target to include the combined static library

Benefits:

• Enables creation of standalone executables with no external runtime dependencies
• Maintains backward compatibility with dynamic linking as fallback
• Simplifies deployment of Codon applications in containerized or restricted environments

The implementation automatically detects the availability of the static runtime and falls back to dynamic linking if not found, ensuring existing workflows remain unaffected.

Test on MacOS:

% ./build/codon build test_openmp.codon
% otool -L test_openmp
test_openmp:
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0)
	/usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.12)
	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1900.180.0)
% ls -l test_openmp
-rwxr-xr-x@ 1 n0madic  staff  1204568 15 лип 21:39 test_openmp
% ./test_openmp
Thread 5Thread 3
Thread 9
Thread 8
Thread 4
Thread 7
Thread 2
Thread 0
Thread 1
Thread 6