Makefile: Remove -gnatg from ADAFLAGS

The `-gnatg` flag (internal GNAT implementation mode) was accidentally
copied over from the flags we use to build libgnat.

Change-Id: I2e9c6d1d5b68168d1608187aad2eae5aead759f9
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/18780
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/Makefile b/Makefile
index 554558a..098c17e 100644
--- a/Makefile
+++ b/Makefile
@@ -34,9 +34,7 @@
 CFLAGS += -fno-common -fomit-frame-pointer
 CFLAGS += -ffunction-sections -fdata-sections
 
-ADAFLAGS += -gnatA -gnatec=$(libhw-dir)/gnat.adc
-ADAFLAGS += -gnatg -gnatp
-ADAFLAGS += $(CFLAGS)
+ADAFLAGS += $(CFLAGS) -gnatA -gnatec=$(libhw-dir)/gnat.adc -gnatp
 # Ada warning options:
 #
 #  a   Activate most optional warnings.