Build also as a shared library

Makefile

@@ -1,13 +1,20 @@
 root_dir := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
+word-dot = $(word $2,$(subst ., ,$1))
 
 TARGET = pg_query
 ARLIB = lib$(TARGET).a
+SOLIB = lib$(TARGET).so
 PGDIR = $(root_dir)/tmp/postgres
 PGDIRBZ2 = $(root_dir)/tmp/postgres.tar.bz2
 
 PG_VERSION = 13.2
+PG_VERSION_MAJOR = $(call word-dot,$(PG_VERSION),1)
 PROTOC_VERSION = 3.14.0
 
+VERSION = 2.0.4
+VERSION_MAJOR = $(call word-dot,$(VERSION),1)
+SONAME = $(SOLIB).$(PG_VERSION_MAJOR)0$(VERSION_MAJOR)
+
 SRC_FILES := $(wildcard src/*.c src/postgres/*.c) vendor/protobuf-c/protobuf-c.c vendor/xxhash/xxhash.c protobuf/pg_query.pb-c.c
 NOT_OBJ_FILES := src/pg_query_enum_defs.o src/pg_query_fingerprint_defs.o src/pg_query_fingerprint_conds.o src/pg_query_outfuncs_defs.o src/pg_query_outfuncs_conds.o src/pg_query_readfuncs_defs.o src/pg_query_readfuncs_conds.o src/postgres/guc-file.o src/postgres/scan.o src/pg_query_json_helper.o
 OBJ_FILES := $(filter-out $(NOT_OBJ_FILES), $(SRC_FILES:.c=.o))
@@ -74,7 +81,7 @@ endif
 
 all: examples test build
 
-build: $(ARLIB)
+build: $(ARLIB) $(SOLIB)
 
 clean:
 	-@ $(RM) $(CLEANLIBS) $(CLEANOBJS) $(CLEANFILES) $(EXAMPLES) $(TESTS)
@@ -146,6 +153,9 @@ extract_source: $(PGDIR)
 $(ARLIB): $(OBJ_FILES) Makefile
 	@$(AR) $@ $(OBJ_FILES)
 
+$(SOLIB): $(OBJ_FILES) Makefile
+	@$(CC) $(CFLAGS) -shared -Wl,-soname,$(SONAME) $(LDFLAGS) -o $@ $(OBJ_FILES) $(LIBS)
+
 protobuf/pg_query.pb-c.c protobuf/pg_query.pb-c.h: protobuf/pg_query.proto
 ifneq ($(shell which protoc-gen-c), )
 	protoc --c_out=. protobuf/pg_query.proto