For a Win32 DLL, a .def file can have a custom executable base:
```
LIBRARY "stub.dll" BASE=0x10000000
```
Currently the parser enforces Base 10, but [Microsoft's
documentation](https://learn.microsoft.com/en-us/cpp/build/reference/rules-for-module-definition-statements?view=msvc-170)
states "Numeric arguments are specified in base 10 or hexadecimal".
This fixes that, and also HEAPSIZE and STACKSIZE (which use the same
function).
There are a few more instances of `getAsInteger` that expect base10 -
for ordinals and the VERSION directive. Since I don't have an
in-the-wild example of a .def file using hexadecimal for these, I am
wary about changing those too.
e9657a12b2