roms: Allow passing configure options to the EDK2 build tools

Since commit f590a812 we build the EDK2 EfiRom utility
unconditionally.

Some distributions require to use extra compiler/linker flags,
i.e. SUSE which enforces the PIE protection (see [*]).

EDK2 build tools already provide a set of variables for that,
use them to allow the caller to easily inject compiler/linker
options..

Now build scripts can pass extra options, example:

  $ make -C roms \
      EDK2_BASETOOLS_OPTFLAGS='-fPIE' \
      efirom

[*] https://lists.opensuse.org/opensuse-factory/2017-06/msg00403.html



Reported-by: Olaf Hering <olaf@aepfle.de>
Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190409134536.15548-3-philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

roms/Makefile

@@ -120,8 +120,21 @@ build-efi-roms: build-pxe-roms
 		$(patsubst %,bin-i386-efi/%.efidrv,$(pxerom_targets)) \
 		$(patsubst %,bin-x86_64-efi/%.efidrv,$(pxerom_targets))
 
+# Build scripts can pass compiler/linker flags to the EDK2 build tools
+# via the EDK2_BASETOOLS_OPTFLAGS (CPPFLAGS and CFLAGS) and
+# EDK2_BASETOOLS_LDFLAGS (LDFLAGS) environment variables.
+#
+# Example:
+#
+#  make -C roms \
+#    EDK2_BASETOOLS_OPTFLAGS='...' \
+#    EDK2_BASETOOLS_LDFLAGS='...' \
+#    efirom
+#
 $(EDK2_EFIROM):
-	$(MAKE) -C edk2/BaseTools
+	$(MAKE) -C edk2/BaseTools \
+		EXTRA_OPTFLAGS='$(EDK2_BASETOOLS_OPTFLAGS)' \
+		EXTRA_LDFLAGS='$(EDK2_BASETOOLS_LDFLAGS)'
 
 slof:
 	$(MAKE) -C SLOF CROSS=$(powerpc64_cross_prefix) qemu