cmake: remove any "$(*_OBJS)" variables when parsing Makefile for sources

To get various lists of files, CMake parses our Makefile looking for
lines matching e.g. "list_var += ...".  In case of LIB_OBJS this
picks up the line "LIB_OBJS += $(COMPAT_OBJS)" as well, so the parsing
macro has a specific instruction to remove "$(COMPAT_OBJS)" from the
resulting list.

Currently this is the only such Makefile variable to be removed from
the list, but the next patches will (re)introduce more variables
containing lists of object files, so let's generalize that removing
instruction to remove any "$(*_OBJS)" Makefile variable as well.

Note that we can't make the pattern matching the Makefile variable too
general, e.g. to match any "$(VARIABLE)", because some lines of our
Makefile do contain variables as directory prefixes, e.g.
"UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o", and we must
definitely keep those.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/buildsystems/CMakeLists.txt

@@ -102,7 +102,7 @@ project(git
 macro(parse_makefile_for_sources list_var makefile regex)
 	file(STRINGS ${makefile} ${list_var} REGEX "^${regex} \\+=(.*)")
 	string(REPLACE "${regex} +=" "" ${list_var} ${${list_var}})
-	string(REPLACE "$(COMPAT_OBJS)" "" ${list_var} ${${list_var}}) #remove "$(COMPAT_OBJS)" This is only for libgit.
+	string(REGEX REPLACE "\\$\\([^)]*_OBJS\\)" "" ${list_var} ${${list_var}}) # remove any "$(*_OBJS)" variables
 	string(STRIP ${${list_var}} ${list_var}) #remove trailing/leading whitespaces
 	string(REPLACE ".o" ".c;" ${list_var} ${${list_var}}) #change .o to .c, ; is for converting the string into a list
 	list(TRANSFORM ${list_var} STRIP) #remove trailing/leading whitespaces for each element in list