util/HugeAllocator: add missing "static inline"

Fixes the non-Linux build.

src/util/HugeAllocator.hxx

@@ -107,7 +107,7 @@ HugeDiscard(void *p, size_t size) noexcept
 
 #include <stdint.h>
 
-WritableBuffer<void>
+static inline WritableBuffer<void>
 HugeAllocate(size_t size)
 {
 	return {new uint8_t[size], size};