ecs-gpu-init: clean up linker flags

`--export-dynamic` is a separate option, independent of `-z`, so pass
it as its own `-Wl` flag.

For consistency, pass the same flags to the external linker.

Signed-off-by: Ben Cressey <bcressey@amazon.com>
(cherry picked from commit 182a188)

packages/ecs-gpu-init/ecs-gpu-init.spec

@@ -21,8 +21,9 @@ cp -r %{_builddir}/sources/%{workspace_name}/* .
 %set_cross_go_flags
 # We don't set `-Wl,-z,now`, because the binary uses lazy loading
 # to load the NVIDIA libraries in the host
-export CGO_LDFLAGS="-Wl,-z,relro,-export-dynamic"
-go build -buildmode=pie -ldflags="${GOLDFLAGS}" -o ecs-gpu-init ./cmd/ecs-gpu-init
+export CGO_LDFLAGS="-Wl,-z,relro -Wl,--export-dynamic"
+export GOLDFLAGS="-compressdwarf=false -linkmode=external -extldflags '${CGO_LDFLAGS}'"
+go build -ldflags="${GOLDFLAGS}" -o ecs-gpu-init ./cmd/ecs-gpu-init
 
 %install
 install -d %{buildroot}%{_cross_bindir}