Enable Windows build for libmodpb64 am: 270cb01386

Original change: https://android-review.googlesource.com/c/platform/external/modp_b64/+/3106174

Change-Id: I3d1de0381f7810d862fb304af56a2590656f95f4
Signed-off-by: Automerger Merge Worker <[email protected]>