Makefile: link gray to libgray

This changes gray to always link to libgray, either statically or dynamically.

Makefile

@@ -45,9 +45,9 @@ MODULES = $(filter-out $(OBJDIR)/main%,$(OBJECTS))
 
 # Build outputs
 GRAY      = $(BINDIR)/gray
-LIBGRAY   = $(LIBDIR)/libgray
+LIBGRAY   = $(LIBDIR)/libgray.so
 BINARIES  = $(GRAY)
-LIBRARIES = $(LIBGRAY).so
+LIBRARIES = $(LIBGRAY)
 
 ##
 ## Git information (used in the version string)
@@ -67,6 +67,7 @@ GIT_DIRTY ?= $(shell test -n "$$(git status --porcelain)" && echo "-dirty")
 FC        = gfortran
 LD        = gfortran
 FFLAGS   += -J$(OBJDIR) -I$(INCDIR) -ffree-line-length-none -fPIC
+LDFLAGS  += -L$(LIBDIR)
 CPPFLAGS += -DREVISION=\"$(GIT_REV)$(GIT_DIRTY)\" -DPREFIX=\"$(PREFIX)\"
 
 ifndef DETERMINISTIC
@@ -78,8 +79,11 @@ endif
 
 # Static build options
 ifdef STATIC
+LIBGRAY := $(LIBGRAY:so=a)
 LIBRARIES := $(LIBRARIES:so=a)
 LDFLAGS += -static
+else
+LDFLAGS += -Wl,-rpath '$$ORIGIN/../lib/'
 endif
 
 # Debug build options
@@ -119,20 +123,20 @@ install: $(BINARIES) $(LIBRARIES) $(SHAREDIR)/doc $(SHAREDIR)/gray.1
 $(OBJDIR)/%.o: $(OBJDIR)/%.d
 
 # GRAY binary
-$(GRAY): $(OBJDIR)/main.o $(LIBGRAY).a | $(BINDIR)
-	$(LD) $(LDFLAGS) -o '$@' $^
+$(GRAY): $(OBJDIR)/main.o $(LIBGRAY) | $(BINDIR)
+	$(LD) $(LDFLAGS) -o '$@' $< -lgray
 
 # GRAY shared library
-$(LIBGRAY).so: $(MODULES) | $(LIBDIR)
+$(LIBDIR)/libgray.so: $(MODULES) | $(LIBDIR)
 	$(LD) -shared $(LDFLAGS) -o '$@' $^
 
 # GRAY static library
-$(LIBGRAY).a($(MODULES)): | $(LIBDIR)
-$(LIBGRAY).a: $(LIBGRAY).a($(MODULES))
+$(LIBDIR)/libgray.a($(MODULES)): | $(LIBDIR)
+$(LIBDIR)/libgray.a: $(LIBDIR)/libgray.a($(MODULES))
 
 # GRAY static library when compiling from JETTO
 -include ../include.mk
-$(JLIBDIR)/libgray.a: $(LIBGRAY).a
+$(JLIBDIR)/libgray.a: $(LIBDIR)/libgray.a
 	install -Dm755 '$<' '$@'
 
 # All documentation