efi_loader: support building UEFI binaries on sandbox

On the sandbox the UEFI binaries must match the host architectures.

Adjust the Makefiles. Provide the PE/COFF header and relocation files.

Allow building helloworld.efi on the sandbox.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/Makefile b/Makefile
index a9a78c3..c746de6 100644
--- a/Makefile
+++ b/Makefile
@@ -17,6 +17,25 @@
 # o Look for make include files relative to root of kernel src
 MAKEFLAGS += -rR --include-dir=$(CURDIR)
 
+# Determine host architecture
+include include/host_arch.h
+MK_ARCH="${shell uname -m}"
+unexport HOST_ARCH
+ifeq ("x86_64", $(MK_ARCH))
+  export HOST_ARCH=$(HOST_ARCH_X86_64)
+else ifneq (,$(findstring $(MK_ARCH), "i386" "i486" "i586" "i686"))
+  export HOST_ARCH=$(HOST_ARCH_X86)
+else ifneq (,$(findstring $(MK_ARCH), "aarch64" "armv8l"))
+  export HOST_ARCH=$(HOST_ARCH_AARCH64)
+else ifeq ("armv7l", $(MK_ARCH))
+  export HOST_ARCH=$(HOST_ARCH_ARM)
+else ifeq ("riscv32", $(MK_ARCH))
+  export HOST_ARCH=$(HOST_ARCH_RISCV32)
+else ifeq ("riscv64", $(MK_ARCH))
+  export HOST_ARCH=$(HOST_ARCH_RISCV64)
+endif
+undefine MK_ARCH
+
 # Avoid funny character set dependencies
 unexport LC_ALL
 LC_COLLATE=C