Makefile: define THIRD_PARTY_SOURCES

Some files in our codebase are borrowed from other projects, and
minimally updated to suit our own needs. We'd sometimes need to tell
our own sources and these third-party sources apart for management
purposes (e.g. we may want to be less strict about coding style and
other issues on third-party files).

Define the $(MAKE) variable THIRD_PARTY_SOURCES that can be used to
match names of third-party sources.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -598,6 +598,7 @@ SCRIPT_SH =
 SCRIPT_LIB =
 TEST_BUILTINS_OBJS =
 TEST_PROGRAMS_NEED_X =
+THIRD_PARTY_SOURCES =
 
 # Having this variable in your environment would break pipelines because
 # you cause "cd" to echo its destination to stdout.  It can also take
@@ -1145,6 +1146,20 @@ BUILTIN_OBJS += builtin/verify-tag.o
 BUILTIN_OBJS += builtin/worktree.o
 BUILTIN_OBJS += builtin/write-tree.o
 
+# THIRD_PARTY_SOURCES is a list of patterns compatible with the
+# $(filter) and $(filter-out) family of functions. They specify source
+# files which are taken from some third-party source where we want to be
+# less strict about issues such as coding style so we don't diverge from
+# upstream unnecessarily (making merging in future changes easier).
+THIRD_PARTY_SOURCES += compat/inet_ntop.c
+THIRD_PARTY_SOURCES += compat/inet_pton.c
+THIRD_PARTY_SOURCES += compat/nedmalloc/%
+THIRD_PARTY_SOURCES += compat/obstack.%
+THIRD_PARTY_SOURCES += compat/poll/%
+THIRD_PARTY_SOURCES += compat/regex/%
+THIRD_PARTY_SOURCES += sha1collisiondetection/%
+THIRD_PARTY_SOURCES += sha1dc/%
+
 GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB)
 EXTLIBS =