[PECOFF] Fix section alignment.

If you have something like

  __declspec(align(8192)) int foo = 1;

in your code, the compiler makes the data to be aligned to 8192-byte
boundary, and the linker align the section containing the data to 8192.

LLD always aligned the section to 4192. So, as long as alignment
requirement is smaller than 4192, it was correct, but for larger
requirements, it's wrong.

This patch fixes the issue.