[SeaBIOS] [PATCH] build: Allow to use cross C preprocessor

[Roman Bolshakov]

An attempt to cross-compile SeaBIOS on macOS can fail because host C
preprocessor doesn't comprehend the command line options:

Compiling IASL src/fw/acpi-dsdt.hex
cpp -P -MD -MT src/fw/acpi-dsdt.hex src/fw/acpi-dsdt.dsl -o out/src/fw/acpi-dsdt.dsl.i.orig
clang: error: no input files
make: *** [src/fw/acpi-dsdt.hex] Error 1

Signed-off-by: Roman Bolshakov 
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index d2d11db..909c0a1 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ OBJCOPY=$(CROSS_PREFIX)objcopy
 OBJDUMP=$(CROSS_PREFIX)objdump
 STRIP=$(CROSS_PREFIX)strip
 PYTHON=python
-CPP=cpp
+CPP=$(CROSS_PREFIX)cpp
 IASL:=iasl
 LD32BIT_FLAG:=-melf_i386