It was being called many times when using backticks.
SDL_DIR = $(SRCDIR)/sdl
SDL_LIB = $(SDL_DIR)/frotz_sdl.a
export SDL_PKGS = libpng libjpeg sdl2 SDL2_mixer freetype2 zlib
-SDL_LDFLAGS += `$(PKG_CONFIG) $(SDL_PKGS) --libs` -lm
+SDL_LDFLAGS += $(shell $(PKG_CONFIG) $(SDL_PKGS) --libs) -lm
DOS_DIR = $(SRCDIR)/dos
#CC = clang
PKG_CONFIG ?= pkg-config
-override CFLAGS += `$(PKG_CONFIG) $(SDL_PKGS) --cflags`
+override CFLAGS += $(shell $(PKG_CONFIG) $(SDL_PKGS) --cflags)
SOURCES = sf_fonts.c sf_msg_en.c sf_resource.c sf_util.c \
sf_deffont.c sf_ftype.c sf_osfdlg.c sf_sig.c sf_video.c \