Fix #1305 - add #ifdef __cplusplus for C++ linkage

Makefile

@@ -47,7 +47,7 @@ mg_prefix: mongoose.c mongoose.h
 # C++ build
 test++: CLANG = g++
 test++: WARN += -Wno-shadow -Wno-missing-field-initializers -Wno-deprecated
-test++: unamalgamated
+test++: test
 
 # Make sure we can build from an unamalgamated sources
 unamalgamated: $(SRCS) $(HDRS) Makefile
@@ -108,7 +108,7 @@ mongoose.c: $(SRCS) Makefile
 	(cat src/license.h; echo; echo '#include "mongoose.h"' ; (for F in src/private.h src/*.c ; do echo; echo '#ifdef MG_ENABLE_LINES'; echo "#line 1 \"$$F\""; echo '#endif'; cat $$F | sed -e 's,#include ".*,,'; done))> $@
 
 mongoose.h: $(HDRS) Makefile
-	(cat src/license.h src/version.h ; cat src/arch.h src/arch_*.h src/config.h src/str.h src/log.h src/timer.h src/util.h src/url.h src/iobuf.h src/base64.h src/md5.h src/sha1.h src/event.h src/net.h src/http.h src/ssi.h src/tls.h src/ws.h src/sntp.h src/mqtt.h src/dns.h | sed -e 's,#include ".*,,' -e 's,^#pragma once,,')> $@
+	(cat src/license.h src/version.h ; cat src/arch.h src/arch_*.h src/config.h src/str.h src/log.h src/timer.h src/util.h src/url.h src/iobuf.h src/base64.h src/md5.h src/sha1.h src/event.h src/net.h src/http.h src/ssi.h src/tls.h src/ws.h src/sntp.h src/mqtt.h src/dns.h | sed -e 's,#include ".*,,' -e 's,^#pragma once,,'; echo; echo '#ifdef __cplusplus'; echo '}'; echo '#endif')> $@
 
 clean: EXAMPLE_TARGET = clean
 clean: ex

mongoose.h

@@ -17,6 +17,10 @@
 #pragma once
 #define MG_VERSION "7.3"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 
 #define MG_ARCH_CUSTOM 0
 #define MG_ARCH_UNIX 1
@@ -959,3 +963,7 @@ bool mg_dns_parse(const uint8_t *buf, size_t len, struct mg_dns_message *);
 size_t mg_dns_parse_rr(const uint8_t *buf, size_t len, size_t ofs,
                        bool is_question, struct mg_dns_rr *);
 size_t mg_dns_decode_name(const uint8_t *, size_t, size_t, char *, size_t);
+
+#ifdef __cplusplus
+}
+#endif

src/version.h

@@ -1,2 +1,6 @@
 #pragma once
 #define MG_VERSION "7.3"
+
+#ifdef __cplusplus
+extern "C" {
+#endif