leveldb: Rename SNAPPY to HAVE_SNAPPY.

This follows the general naming convention for preprocessor macros used
to detect feature (library / header file / symbol) presence.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171184641

build_detect_platform

@@ -21,8 +21,8 @@
 # The PLATFORM_CCFLAGS and PLATFORM_CXXFLAGS might include the following:
 #
 #       -DLEVELDB_ATOMIC_PRESENT     if <atomic> is present
-#       -DLEVELDB_PLATFORM_POSIX     for Posix-based platforms
-#       -DSNAPPY                     if the Snappy library is present
+#       -DLEVELDB_PLATFORM_POSIX=1   for Posix-based platforms
+#       -DHAVE_SNAPPY=1              if the Snappy library is present
 #
 
 OUTPUT=$1
@@ -133,7 +133,7 @@ case "$TARGET_OS" in
         ;;
     OS_ANDROID_CROSSCOMPILE)
         PLATFORM=OS_ANDROID
-        COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_ANDROID -DLEVELDB_PLATFORM_POSIX"
+        COMMON_FLAGS="$MEMCMP_FLAG -D_REENTRANT -DOS_ANDROID -DLEVELDB_PLATFORM_POSIX=1"
         PLATFORM_LDFLAGS=""  # All pthread features are in the Android C library
         PORT_FILE=port/port_posix.cc
         PORT_SSE_FILE=port/port_posix_sse.cc
@@ -196,10 +196,10 @@ else
       int main() {}
 EOF
     if [ "$?" = 0 ]; then
-        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX -DLEVELDB_ATOMIC_PRESENT"
+        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX=1 -DLEVELDB_ATOMIC_PRESENT"
         PLATFORM_CXXFLAGS="-std=c++0x"
     else
-        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX"
+        COMMON_FLAGS="$COMMON_FLAGS -DLEVELDB_PLATFORM_POSIX=1"
     fi
 
     # Test whether Snappy library is installed
@@ -209,7 +209,7 @@ EOF
       int main() {}
 EOF
     if [ "$?" = 0 ]; then
-        COMMON_FLAGS="$COMMON_FLAGS -DSNAPPY"
+        COMMON_FLAGS="$COMMON_FLAGS -DHAVE_SNAPPY=1"
         PLATFORM_LIBS="$PLATFORM_LIBS -lsnappy"
     fi
 

port/port_posix.h

@@ -39,9 +39,9 @@
 #endif
 
 #include <pthread.h>
-#ifdef SNAPPY
+#ifdef HAVE_SNAPPY
 #include <snappy.h>
-#endif
+#endif  // defined(HAVE_SNAPPY)
 #include <stdint.h>
 #include <string>
 #include "port/atomic_pointer.h"
@@ -106,33 +106,33 @@ extern void InitOnce(OnceType* once, void (*initializer)());
 
 inline bool Snappy_Compress(const char* input, size_t length,
                             ::std::string* output) {
-#ifdef SNAPPY
+#ifdef HAVE_SNAPPY
   output->resize(snappy::MaxCompressedLength(length));
   size_t outlen;
   snappy::RawCompress(input, length, &(*output)[0], &outlen);
   output->resize(outlen);
   return true;
-#endif
+#endif  // defined(HAVE_SNAPPY)
 
   return false;
 }
 
 inline bool Snappy_GetUncompressedLength(const char* input, size_t length,
                                          size_t* result) {
-#ifdef SNAPPY
+#ifdef HAVE_SNAPPY
   return snappy::GetUncompressedLength(input, length, result);
 #else
   return false;
-#endif
+#endif  // defined(HAVE_SNAPPY)
 }
 
 inline bool Snappy_Uncompress(const char* input, size_t length,
                               char* output) {
-#ifdef SNAPPY
+#ifdef HAVE_SNAPPY
   return snappy::RawUncompress(input, length, output);
 #else
   return false;
-#endif
+#endif  // defined(HAVE_SNAPPY)
 }
 
 inline bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg) {