Clean up C++ support

Use symlinks instead of include hack to build a file as both C and
C++.

Author: riptl

src/util/tile/Local.mk

@@ -6,7 +6,7 @@ $(call run-unit-test,test_cpuset)
 ifdef FD_HAS_CXX
 $(call add-objs,fd_tile_threads_cxx,fd_util)
 else
-$(call add-objs,fd_tile_threads,fd_util)
+$(call add-objs,fd_tile_threads_c,fd_util)
 endif
 else
 $(call add-objs,fd_tile_nothreads,fd_util)

src/util/tile/fd_tile_threads.c

@@ -0,0 +1 @@
+fd_tile_threads.c

src/util/tile/fd_tile_threads.inc src/util/tile/fd_tile_threads_c.csrc/util/tile/fd_tile_threads.inc renamed to src/util/tile/fd_tile_threads_c.c

@@ -2,7 +2,7 @@ $(call add-hdrs,fd_tpool.h fd_map_reduce.h)
 ifdef FD_HAS_CXX
 $(call add-objs,fd_tpool_cxx,fd_util)
 else
-$(call add-objs,fd_tpool,fd_util)
+$(call add-objs,fd_tpool_c,fd_util)
 endif
 $(call make-unit-test,test_tpool,test_tpool,fd_util)
 

src/util/tile/fd_tile_threads_cxx.cxx

@@ -0,0 +1 @@
+fd_tpool.c