caffe2: fix gcc8 warnings

Summary:
The warnings are erroneous as far as i can see,
so tweak things to avoid. The (unsigned int) cast is
to avoid passing -1 to a size_t time.  This was triggered
in gcc8's lto build only, giving:

  caffe2/aten/src/TH/generic/THTensor.cpp: In function ‘THFloatTensor_squeeze1d’:
  lto1: error: ‘__builtin_memset’ specified size 18446744073709551608
  exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
  In function ‘newImpl’,
    inlined from ‘operator new’ at common/memory/OperatorOverride.cpp:86:23,
    inlined from ‘allocate’ at third-party-buck/platform007/build/libgcc/include/c++/7.3.0/ext/new_allocator.h:111:0,
    inlined from ‘allocate’ at third-party-buck/platform007/build/libgcc/include/c++/7.3.0/bits/alloc_traits.h:436:0,
    inlined from ‘_M_allocate’ at third-party-buck/platform007/build/libgcc/include/c++/7.3.0/bits/stl_vector.h:172:0,
    inlined from ‘_M_default_append’ at third-party-buck/platform007/build/libgcc/include/c++/7.3.0/bits/vector.tcc:571:0,
    inlined from ‘resize’ at third-party-buck/platform007/build/libgcc/include/c++/7.3.0/bits/stl_vector.h:671:0,
    inlined from ‘THTensor_resizeDim’ at caffe2/aten/src/TH/THTensor.hpp:123:0,
    inlined from ‘THFloatTensor_squeeze1d.part.198’ at caffe2/aten/src/TH/generic/THTensor.cpp:429:0,
    inlined from ‘THFloatTensor_squeeze1d’:
  common/memory/OperatorOverride.cpp:86:23: error:
  argument 1 value ‘18446744073709551608’ exceeds maximum object size 9223372036854775807 [-Werror=alloc-size-larger-than=]
   void* ptr = malloc(size);

Reviewed By: soumith

Differential Revision: D9568621

fbshipit-source-id: 4569a4be897d669caa3f283f4b84ec829e8d77ad

aten/src/TH/generic/THTensor.cpp

@@ -337,7 +337,7 @@ void THTensor_(select)(THTensor *self, THTensor *src, int dimension, int64_t sli
     self->set_size(d, self->size(d+1));
     self->set_stride(d, self->stride(d+1));
   }
-  self->resize_dim(self->dim() - 1);
+  self->resize_dim((unsigned int)(self->dim() - 1));
 }
 
 void THTensor_(transpose)(THTensor *self, THTensor *src, int dimension1, int dimension2)
@@ -444,7 +444,7 @@ void THTensor_(squeeze1d)(THTensor *self, THTensor *src, int dimension)
       self->set_size(d, self->size(d+1));
       self->set_stride(d, self->stride(d+1));
     }
-    self->resize_dim(self->dim() - 1);
+    self->resize_dim((unsigned int)(self->dim() - 1));
   }
 }
 

aten/src/THC/THCTensor.cpp

@@ -227,7 +227,7 @@ void THCTensor_squeeze1d(THCState *state, THCTensor *self, THCTensor *src, int d
       self->set_size(d, self->size(d+1));
       self->set_stride(d, self->stride(d+1));
     }
-    self->resize_dim(self->dim() - 1);
+    self->resize_dim((unsigned int)(self->dim() - 1));
   }
 }
 

aten/src/THC/generic/THCTensor.cpp

@@ -354,7 +354,7 @@ void THCTensor_(select)(THCState *state, THCTensor *self, THCTensor *src, int di
     self->set_size(d, self->size(d+1));
     self->set_stride(d, self->stride(d+1));
   }
-  self->resize_dim(self->dim() - 1);
+  self->resize_dim((unsigned int)(self->dim() - 1));
 }
 
 void THCTensor_(transpose)(THCState *state, THCTensor *self, THCTensor *src, int dimension1, int dimension2)