tests/tcg: mark test-vma as a linux-only test

The main multiarch tests should compile for any POSIX system, however
test-vma's usage of MAP_NORESERVE makes it a linux-only test. Simply
moving the source file is enough for the build logic to skip on BSD's.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-14-alex.bennee@linaro.org>

diff --git a/tests/tcg/multiarch/test-vma.c b/tests/tcg/multiarch/linux/test-vma.c
similarity index 100%
rename from tests/tcg/multiarch/test-vma.c
rename to tests/tcg/multiarch/linux/test-vma.c