xrow: rename xrow.cc -> xrow.c

Part of #2507

src/box/CMakeLists.txt

@@ -24,7 +24,7 @@ add_library(box STATIC
     iproto_constants.c
     errcode.c
     error.cc
-    xrow.cc
+    xrow.c
     xrow_io.cc
     xlog.cc
     tuple_format.c

test/unit/CMakeLists.txt

@@ -60,7 +60,7 @@ add_executable(vclock.test vclock.cc unit.c
     ${CMAKE_SOURCE_DIR}/src/histogram.c)
 target_link_libraries(vclock.test core salad small)
 add_executable(xrow.test xrow.cc unit.c
-    ${CMAKE_SOURCE_DIR}/src/box/xrow.cc
+    ${CMAKE_SOURCE_DIR}/src/box/xrow.c
     ${CMAKE_SOURCE_DIR}/src/box/vclock.c
     ${CMAKE_SOURCE_DIR}/src/box/iproto_constants.c
     ${CMAKE_SOURCE_DIR}/src/box/errcode.c