m4/sage_spkg_collect.m4: Handle 'dependencies_build' files, generate …

…Makefile variables build_deps_...

build/make/Makefile.in

@@ -538,7 +538,7 @@ debug-check:
 #     $(1): package name
 pkg_deps = \
 	$(if $(filter gcc,$(1)),,$$(GCC_DEP))\
-	$(foreach dep,$(deps_$(1)),\
+	$(foreach dep,$(build_deps_$(1)),\
         $(if $(value inst_$(dep)),$$(inst_$(dep)),$(dep)))
 
 # ============================= normal packages ==============================

m4/sage_spkg_collect.m4

@@ -352,24 +352,31 @@ AC_DEFUN([SAGE_SPKG_FINALIZE], [dnl
     ], [dnl
         AS_VAR_SET([DEPS], [])
     ])
+    AS_IF([test -f "$DIR/dependencies_build"], [dnl
+        dnl - the # symbol is treated as comment which is removed
+        AS_VAR_SET([BUILD_DEPS], [`sed 's/^ *//; s/ *#.*//; q' $DIR/dependencies_build`])
+    ], [dnl
+        dnl No 'dependencies_build' file, so reuse 'dependencies' for that
+        AS_VAR_COPY([BUILD_DEPS], [DEPS])
+    ])
     AS_IF([test -f "$DIR/dependencies_optional"], [dnl
         for a in $(sed 's/^ *//; s/ *#.*//; q' "$DIR/dependencies_optional"); do
-            AS_VAR_APPEND([DEPS], [' $(findstring '$a',$(OPTIONAL_INSTALLED_PACKAGES)) '])
+            AS_VAR_APPEND([BUILD_DEPS], [' $(findstring '$a',$(OPTIONAL_INSTALLED_PACKAGES)) '])
         done
     ])
-    AS_CASE(["$DEPS"], [*\|*], [], [AS_VAR_APPEND([DEPS], [" |"])])
+    AS_CASE(["$BUILD_DEPS"], [*\|*], [], [AS_VAR_APPEND([BUILD_DEPS], [" |"])])
     AS_IF([test -f "$DIR/dependencies_order_only"], [dnl
         ADD_DEPS=$(echo $(sed 's/^ *//; s/ *#.*//; q' $DIR/dependencies_order_only))
-        AS_VAR_APPEND([DEPS], [" $ADD_DEPS"])
+        AS_VAR_APPEND([BUILD_DEPS], [" $ADD_DEPS"])
     ], [dnl
-        m4_case(SPKG_SOURCE, [pip], [AS_VAR_APPEND([DEPS], [' pip'])], [:])dnl
+        m4_case(SPKG_SOURCE, [pip], [AS_VAR_APPEND([BUILD_DEPS], [' pip'])], [:])dnl
     ])
     AS_IF([test -f "$DIR/dependencies_check"], [dnl
         ADD_DEPS=$(echo $(sed 's/^ *//; s/ *#.*//; q' $DIR/dependencies_check))
-        AS_VAR_APPEND([DEPS], [' $(and $(filter-out no,$(SAGE_CHECK_]SPKG_NAME[)), '"$ADD_DEPS"')'])dnl
+        AS_VAR_APPEND([BUILD_DEPS], [' $(and $(filter-out no,$(SAGE_CHECK_]SPKG_NAME[)), '"$ADD_DEPS"')'])dnl
     ])
     dnl
-    SAGE_PACKAGE_DEPENDENCIES="${SAGE_PACKAGE_DEPENDENCIES}$(printf '\ndeps_')SPKG_NAME = ${DEPS}"
+    SAGE_PACKAGE_DEPENDENCIES="${SAGE_PACKAGE_DEPENDENCIES}$(printf '\ndeps_')SPKG_NAME = ${DEPS}$(printf '\nbuild_deps_')SPKG_NAME = ${BUILD_DEPS}"
     dnl
     dnl Determine package build rules
     m4_case(SPKG_SOURCE,