Compile error on ARMv7 platform

[alexcherut]

ghoscript builds all the sources (including brotli) using -Werror=declaration-after-statement which causes build failure of brotli/c/dec/decode.c when targeting ARMv7 platform.

That's because PreloadSymbol() starts with a statement followed by BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD() macro which on ARMv7 expands to variable declaration.

See https://bugs.ghostscript.com/show_bug.cgi?id=708831 for details and a proposed patch.