build: reduce binary size by adding -s -w to ldflags

[chenrui333]

Add -s (omit symbol table and debug info) and -w (omit DWARF debug info) to linker flags to minimize the size of the generated binaries.

## before

$ ls -alh /opt/homebrew/Cellar/malcontent/1.6.0/bin/mal
-r-xr-xr-x  1 rui  wheel    37M Dec 17 15:44 /opt/homebrew/Cellar/malcontent/1.6.0/bin/mal

## after

$ ls -alh /opt/homebrew/Cellar/malcontent/1.6.0/bin/mal
-r-xr-xr-x  1 rui  wheel    32M Dec 17 15:45 /opt/homebrew/Cellar/malcontent/1.6.0/bin/mal

relates to Homebrew/homebrew-core#201530

[egibs]

Thanks!