makefile: adjust linker path in Makefile

As mentioned in https://github.com/projectacrn/acrn-documentation/pull/38
on some operating systems, the ``gnu-efi`` package installs the
linker under a ``gnuefi`` folder in ``${LIBDIR}``. This is the
case in Fedora for example. Check if the gnuefi folder is there
and use it if it is in the path to the linker.  This PR fixes the
Makefile rather than documenting how to edit it yourself.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

Author: dbkinder

hypervisor/bsp/uefi/efi/Makefile

@@ -55,8 +55,15 @@ endif
 INCDIR := /usr/include
 
 # gnuefi sometimes installs these under a gnuefi/ directory, and sometimes not
-CRT0 := $(LIBDIR)/crt0-efi-$(ARCH).o
-LDSCRIPT := $(LIBDIR)/elf_$(ARCH)_efi.lds
+ifneq ("$(wildcard $(LIBDIR)/gnuefi/crt0-efi-$(ARCH).o)","")
+	CRT0 := $(LIBDIR)/gnuefi/crt0-efi-$(ARCH).o
+	LDSCRIPT := $(LIBDIR)/gnuefi/elf_$(ARCH)_efi.lds
+else
+	CRT0 := $(LIBDIR)/crt0-efi-$(ARCH).o
+	LDSCRIPT := $(LIBDIR)/elf_$(ARCH)_efi.lds
+endif
+
+
 
 CFLAGS=-I. -I.. -I$(INCDIR)/efi -I$(INCDIR)/efi/$(ARCH) \
 		-DEFI_FUNCTION_WRAPPER -fPIC -fshort-wchar -ffreestanding \