build: Drop no longer needed `-fvisibility=hidden` compiler option

build: Drop no longer needed `-fvisibility=hidden` compiler option

cmake: Fix passing `SECP256K1_APPEND_CFLAGS` to clang-cl

This change also makes the compile invocation string more natural by
ensuring flags do not follow source files.

Linker flags are also amended for consistency.

cmake: Fix passing `SECP256K1_APPEND_CFLAGS` to clang-cl

This change also makes the compile invocation string more natural by
ensuring flags do not follow source files.

cmake: Fix passing `SECP256K1_APPEND_CFLAGS` to clang-cl

This change also makes the compile invocation string more natural by
ensuring flags do not follow source files.

ci: Add new "Windows (clang-cl)" job

libsecp256k1 0.6.0

build: Drop no longer needed `-fvisibility=hidden` compiler option

build: Drop no longer needed `-fvisibility=hidden` compiler option

build: Drop no longer needed `-fvisibility=hidden` compiler option