build: fix linker flags on Windows

build: fix linker flags on Windows

The --export-dynamic linker option is only applicable to ELF.
On Windows, where COFF is used, it causes warnings:

    x86_64-w64-mingw32-ld: warning: --export-dynamic is not supported
    for PE+ targets, did you mean --export-all-symbols? (MinGW)

    LINK : warning LNK4044: unrecognized option '/-export-dynamic';
    ignored (clang)

Don't add --export-dynamic on Windows anywhere.

Fixes: b031e13d7f0d ("build: fix plugin load on static build")
Cc: stable@dpdk.org
Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
Acked-by: Ranjit Menon <ranjit.menon@intel.com>