linux-user: Rewrite mmap_frag

Use 'last' variables instead of 'end' variables.
Always zero MAP_ANONYMOUS fragments, which we previously
failed to do if they were not writable; early exit in case
we allocate a new page from the kernel, known zeros.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230707204054.8792-16-richard.henderson@linaro.org>
1 file changed