Fix build for UCLIBC platforms

src/core/SkVarAlloc.cpp

 #include "SkVarAlloc.h"
 
 // We use non-standard malloc diagnostic methods to make sure our allocations are sized well.
 #if defined(SK_BUILD_FOR_MAC)
     #include <malloc/malloc.h>
 #elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_WIN32)
     #include <malloc.h>
 #endif
 
 struct SkVarAlloc::Block {
@@ skipping 29 matching lines @@
     size_t alloc = 1<<fLgSize++;
     while (alloc < bytes + sizeof(Block)) {
         alloc *= 2;
     }
     fBlock = Block::Alloc(fBlock, alloc, flags);
     fByte = fBlock->data();
     fRemaining = alloc - sizeof(Block);
 
 #if defined(SK_BUILD_FOR_MAC)
     SkASSERT(alloc == malloc_good_size(alloc));
-#elif defined(SK_BUILD_FOR_UNIX)
+#elif defined(SK_BUILD_FOR_UNIX) && !defined(__UCLIBC__)
     // TODO(mtklein): tune so we can assert something like this
     //SkASSERT(alloc == malloc_usable_size(fBlock));
 #endif
 }
 
 static size_t heap_size(void* p) {
 #if defined(SK_BUILD_FOR_MAC)
     return malloc_size(p);
-#elif defined(SK_BUILD_FOR_UNIX)
+#elif defined(SK_BUILD_FOR_UNIX) && !defined(__UCLIBC__)
     return malloc_usable_size(p);
 #elif defined(SK_BUILD_FOR_WIN32)
     return _msize(p);
 #else
     return 0;  // Tough luck.
 #endif
 }
 
 size_t SkVarAlloc::approxBytesAllocated() const {
     size_t sum = 0;
     for (Block* b = fBlock; b; b = b->prev) {
         sum += heap_size(b);
     }
     return sum;
 }