build: Unbreak Meson build on FreeBSD (#3549)

* generateVersion.sh: move cp(1) flags before arguments

POSIX and BSD cp(1) don't support flags after arguments e.g.,

cp: -fr is not a directory

* generateVersion.sh: switch to sed(1) -i for better compatibility

On BSDs awk is usually The One True Awk thus doesn't support `-i inplace`.

awk: unknown option -i ignored
awk: can't open file {sub(/@HASH@/,"1234567890abcdef")}1
 source line number 1