Merge #52: build: add MINISKETCH_INCLUDE_DIR_INT variable

84a121c build: add MINISKETCH_INCLUDE_DIR_INT variable (fanquake)

Pull request description:

  Just a convenient way for downstream projects to use the include dir. Similar to what we have in the Univalue subtree now.

  cc theuni

ACKs for top commit:
  sipa:
    utACK 84a121c

Tree-SHA512: 226a350f2b8f08695e9c3934bda501242e4ceb0ff61680ee20302eb533aae4db5cae09ef700fe3250282ef60a412f460853c208db23c2bef7b58466a18ce3fc8

Author: sipa

sources.mk

@@ -8,6 +8,8 @@
 #   downstreams to use these variables without having to manually account for
 #   the path change.
 
+MINISKETCH_INCLUDE_DIR_INT = %reldir%/include
+
 MINISKETCH_DIST_HEADERS_INT =
 MINISKETCH_DIST_HEADERS_INT += %reldir%/include/minisketch.h