compiler: fix data section alignment in the wasm NCG

Previously we tried to lower the alignment requirement as far as possible, based on the section kind inferred from the CLabel. For info tables, .p2align 1 was applied given the GC should only need the lowest bit to tag forwarding pointers. But this would lead to unaligned loads/stores, which has a performance penalty even if the wasm spec permits it. Furthermore, the test suite has shown memory corruption in a few cases when compacting gc is used.

This patch takes a more conservative approach: all data sections except C strings align to word size.