rocksdb: fix make unity

Summary:
changed make unity target to use $LIB_SOURCES as a source of library source code. In the old way (using find) table/mock_table.h was added to a list of library objects and this was a course of `make unity` break.

`build_tools/unity` contains some redundant code, I deleted it and moved the functionality in the Makefile.

Test Plan:
Make sure unity completes with no errors.
```lang=bash
% make unity
```

Reviewers: sdong, rven, igor, meyering

Reviewed By: igor, meyering

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35385

Makefile

@@ -378,7 +378,13 @@ analyze: clean
 		$(MAKE) dbg
 
 unity.cc:
-	$(shell (export ROCKSDB_ROOT="$(CURDIR)"; "$(CURDIR)/build_tools/unity" "$(CURDIR)/unity.cc"))
+	rm -f $@ $@-t
+	for source_file in $(LIB_SOURCES); do \
+		echo "#include <$$source_file>" >> $@-t; \
+	done
+	echo 'int main(int argc, char** argv){ return 0; }' >> $@-t
+	chmod a=r $@-t
+	mv $@-t $@
 
 unity: unity.o
 	$(AM_LINK)

build_tools/unity

@@ -1,78 +0,0 @@
-#!/bin/sh
-#
-# Create the unity file
-#
-
-OUTPUT=$1
-if test -z "$OUTPUT"; then
-  echo "usage: $0 <output-filename>" >&2
-  exit 1
-fi
-
-# Delete existing file, if it exists
-rm -f "$OUTPUT"
-touch "$OUTPUT"
-
-# Detect OS
-if test -z "$TARGET_OS"; then
-    TARGET_OS=`uname -s`
-fi
-
-# generic port files (working on all platform by #ifdef) go directly in /port
-GENERIC_PORT_FILES=`cd "$ROCKSDB_ROOT"; find port -name '*.cc' | tr "\n" " "`
-
-# On GCC, we pick libc's memcmp over GCC's memcmp via -fno-builtin-memcmp
-case "$TARGET_OS" in
-    Darwin)
-        # PORT_FILES=port/darwin/darwin_specific.cc
-        ;;
-    IOS)
-        ;;
-    Linux)
-        # PORT_FILES=port/linux/linux_specific.cc
-        ;;
-    SunOS)
-        # PORT_FILES=port/sunos/sunos_specific.cc
-        ;;
-    FreeBSD)
-        # PORT_FILES=port/freebsd/freebsd_specific.cc
-        ;;
-    NetBSD)
-        # PORT_FILES=port/netbsd/netbsd_specific.cc
-        ;;
-    OpenBSD)
-        # PORT_FILES=port/openbsd/openbsd_specific.cc
-        ;;
-    DragonFly)
-        # PORT_FILES=port/dragonfly/dragonfly_specific.cc
-        ;;
-    OS_ANDROID_CROSSCOMPILE)
-        # PORT_FILES=port/android/android.cc
-        ;;
-    *)
-        echo "Unknown platform!" >&2
-        exit 1
-esac
-
-# We want to make a list of all cc files within util, db and table
-# except for the test and benchmark files. By default, find will output a list
-# of all files matching either rule, so we need to append -print to make the
-# prune take effect.
-DIRS="util db table utilities"
-
-set -f # temporarily disable globbing so that our patterns arent expanded
-PRUNE_TEST="-name *test*.cc -prune"
-PRUNE_BENCH="-name *bench*.cc -prune"
-PORTABLE_FILES=`cd "$ROCKSDB_ROOT"; find $DIRS $PRUNE_TEST -o $PRUNE_BENCH -o -name '*.cc' -print | sort`
-PORTABLE_CPP=`cd "$ROCKSDB_ROOT"; find $DIRS $PRUNE_TEST -o $PRUNE_BENCH -o -name '*.cpp' -print | sort`
-set +f # re-enable globbing
-
-# The sources consist of the portable files, plus the platform-specific port
-# file.
-for SOURCE_FILE in $PORTABLE_FILES $GENERIC_PORT_FILES $PORT_FILES $PORTABLE_CPP
-do
-	echo "#include <$SOURCE_FILE>" >> "$OUTPUT"
-done
-
-echo "int main(int argc, char** argv){ return 0; }" >> "$OUTPUT"
-