Build: Log when test -f fails in Makefile

Silently emitting an error makes it a bit harder to debug. Instead,
print a helpful log message to point the developer in the right
direction.

Alternatively this could have been implemented by just removing the
recipe echo suppression (@), but the subsequent make output became too
noisy.

Author: TheCharlatan

src/Makefile.am

@@ -1030,7 +1030,7 @@ clean-local:
 	-rm -rf test/__pycache__
 
 .rc.o:
-	@test -f $(WINDRES)
+	@test -f $(WINDRES) || (echo "windres $(WINDRES) not found, but is required to compile windows resource files"; exit 1)
 	## FIXME: How to get the appropriate modulename_CPPFLAGS in here?
 	$(AM_V_GEN) $(WINDRES) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(CPPFLAGS) -DWINDRES_PREPROC -i $< -o $@
 

src/Makefile.qt.include

@@ -371,13 +371,13 @@ translate: $(srcdir)/qt/bitcoinstrings.cpp $(QT_FORMS_UI) $(QT_FORMS_UI) $(BITCO
 	@rm -f $(srcdir)/qt/locale/bitcoin_en.xlf.old
 
 $(QT_QRC_LOCALE_CPP): $(QT_QRC_LOCALE) $(QT_QM)
-	@test -f $(RCC)
+	@test -f $(RCC) || (echo "rcc $(RCC) not found, but is required for generating qrc cpp files"; exit 1)
 	@cp -f $< $(@D)/temp_$(<F)
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(RCC) -name bitcoin_locale --format-version 1 $(@D)/temp_$(<F) > $@
 	@rm $(@D)/temp_$(<F)
 
 $(QT_QRC_CPP): $(QT_QRC) $(QT_FORMS_H) $(QT_RES_FONTS) $(QT_RES_ICONS) $(QT_RES_ANIMATION)
-	@test -f $(RCC)
+	@test -f $(RCC) || (echo "rcc $(RCC) not found, but is required for generating qrc cpp files"; exit 1)
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(RCC) -name bitcoin --format-version 1 $< > $@
 
 CLEAN_QT = $(nodist_qt_libbitcoinqt_a_SOURCES) $(QT_QM) $(QT_FORMS_H) qt/*.gcda qt/*.gcno qt/temp_bitcoin_locale.qrc
@@ -404,7 +404,7 @@ bitcoin_qt_apk: FORCE
 	cd qt/android && ./gradlew build
 
 ui_%.h: %.ui
-	@test -f $(UIC)
+	@test -f $(UIC) || (echo "uic $(UIC) not found, but is required for generating ui headers"; exit 1)
 	@$(MKDIR_P) $(@D)
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(UIC) -o $@ $< || (echo "Error creating $@"; false)
 
@@ -415,6 +415,6 @@ moc_%.cpp: %.h
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(MOC) $(DEFAULT_INCLUDES) $(QT_INCLUDES_UNSUPPRESSED) $(MOC_DEFS) $< > $@
 
 %.qm: %.ts
-	@test -f $(LRELEASE)
+	@test -f $(LRELEASE) || (echo "lrelease $(LRELEASE) not found, but is required for generating translations"; exit 1)
 	@$(MKDIR_P) $(@D)
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(LRELEASE) -silent $< -qm $@