src: namespace symbols clashing with lib

Before this patch `lib/http.h` and `src/tool_sdecls.h` both declared
`HTTPREQ_*` enums.

Rename `src` ones to have distinct names.

They are not included in the same code for now, but this may change when
bundling unit/libtests into single programs.

Closes #14785

src/tool_sdecls.h

@@ -114,12 +114,12 @@ typedef enum {
  */
 
 typedef enum {
-  HTTPREQ_UNSPEC,  /* first in list */
-  HTTPREQ_GET,
-  HTTPREQ_HEAD,
-  HTTPREQ_MIMEPOST,
-  HTTPREQ_SIMPLEPOST,
-  HTTPREQ_PUT
+  TOOL_HTTPREQ_UNSPEC,  /* first in list */
+  TOOL_HTTPREQ_GET,
+  TOOL_HTTPREQ_HEAD,
+  TOOL_HTTPREQ_MIMEPOST,
+  TOOL_HTTPREQ_SIMPLEPOST,
+  TOOL_HTTPREQ_PUT
 } HttpReq;