Fix: [Cygwin] Fix missing definitions in stdafx

Fix the following compile errors:

In file included from openttd/src/debug.h:15:0,
from openttd/src/string.cpp:13:
openttd/src/cpu.h:35:19: error: 'uint' was not declared in this scope
bool HasCPUIDFlag(uint type, uint index, uint bit);

openttd/src/string.cpp: In function 'char* strcasestr(const char*, const char*)':
openttd/src/string.cpp:548:7: error: 'strncasecmp' was not declared in this scope
if (strncasecmp(haystack, needle, needle_len) == 0) return const_cast<char *>(haystack);

openttd/src/strgen/strgen_base.cpp: In function 'void EmitPlural(Buffer*, char*, int)':
openttd/src/core/alloc_func.hpp:136:6: error: 'alloca' was not declared in this scope
(T*)alloca((num_elements) * sizeof(T)))

Signed-off-by: Joe Stringer <joe@wand.net.nz>