Fix deprecated CreateGEP/CreateLoad usage

[eush77]

/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/MixContext.cpp:163:23: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                   B->CreateGEP(Table, B->getInt32(Index)));
                      ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/MixContext.cpp:311:27: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                       B->CreateGEP(Params, B->getInt32(ParamIndex)));
                          ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/MixContext.cpp:341:27: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                       B->CreateGEP(Elements, B->getInt32(ElNum)));
                          ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/MixContext.cpp:412:22: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
      B.CreateLoad(B.CreateGEP(TP, B.getInt32(Index)), getName(VD)),
                     ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/MixContext.cpp:412:9: warning: 'CreateLoad' is deprecated: Use the version that explicitly specifies the loaded type instead [-Wdeprecated-declarations]
      B.CreateLoad(B.CreateGEP(TP, B.getInt32(Index)), getName(VD)),
        ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/StagedIRBuilder.h:884:25: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                      B.CreateGEP(Words, B.getInt32(WN)));
                        ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/StagedIRBuilder.h:941:25: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                      B.CreateGEP(Elements, B.getInt32(ElNum)));
                        ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/StagedIRBuilder.h:481:41: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
    B.CreateStore(SB.stage(*IIter++), B.CreateGEP(Indices, B.getInt32(INum)));
                                        ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/StagedIRBuilder.h:423:21: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                  B.CreateGEP(Args, B.getInt32(ArgNum)));
                    ^
/home/eush/src/grad/llvm-mix/llvm/lib/Transforms/Mix/StagedIRBuilder.h:649:21: warning: 'CreateGEP' is deprecated: Use the version with explicit element type instead [-Wdeprecated-declarations]
                  B.CreateGEP(Vals, B.getInt32(OpNum)));
                    ^