Makefile: Add option to use toolchain default ABI and ISA string

When PLATFORM_RISCV_ABI and PLATFORM_RISCV_ISA are not specified,
we force "-mabi=lp64 -march=rv64gc" for RV64 and force "-mabi=ilp32
-march=rv32gc" for RV32. This can prevent users from using the
toolchain default "-mabi" and "-march" options.

To allow using toolchain defaults, we add compile-time option
PLATFORM_RISCV_TOOLCHAIN_DEFAULT which when enabled forces the
top-level makefile to use toolchain default ABI and ISA string.

To enable the option, pass "PLATFORM_RISCV_TOOLCHAIN_DEFAULT=1"
to top-level make.

Reported-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Makefile

@@ -94,6 +94,8 @@ DTC		=	dtc
 
 # Guess the compillers xlen
 OPENSBI_CC_XLEN := $(shell TMP=`$(CC) -dumpmachine | sed 's/riscv\([0-9][0-9]\).*/\1/'`; echo $${TMP})
+OPENSBI_CC_ABI := $(shell TMP=`$(CC) -v 2>&1 | sed -n 's/.*\(with\-abi=\([a-zA-Z0-9]*\)\).*/\2/p'`; echo $${TMP})
+OPENSBI_CC_ISA := $(shell TMP=`$(CC) -v 2>&1 | sed -n 's/.*\(with\-arch=\([a-zA-Z0-9]*\)\).*/\2/p'`; echo $${TMP})
 
 # Setup platform XLEN
 ifndef PLATFORM_RISCV_XLEN
@@ -143,14 +145,22 @@ deps-y+=$(firmware-objs-path-y:.o=.dep)
 
 # Setup platform ABI, ISA and Code Model
 ifndef PLATFORM_RISCV_ABI
+  ifneq ($(PLATFORM_RISCV_TOOLCHAIN_DEFAULT), 1)
     ifeq ($(PLATFORM_RISCV_XLEN), 32)
       PLATFORM_RISCV_ABI = ilp$(PLATFORM_RISCV_XLEN)
     else
       PLATFORM_RISCV_ABI = lp$(PLATFORM_RISCV_XLEN)
     endif
+  else
+    PLATFORM_RISCV_ABI = $(OPENSBI_CC_ABI)
+  endif
 endif
 ifndef PLATFORM_RISCV_ISA
+  ifneq ($(PLATFORM_RISCV_TOOLCHAIN_DEFAULT), 1)
     PLATFORM_RISCV_ISA = rv$(PLATFORM_RISCV_XLEN)imafdc
+  else
+    PLATFORM_RISCV_ISA = $(OPENSBI_CC_ISA)
+  endif
 endif
 ifndef PLATFORM_RISCV_CODE_MODEL
   PLATFORM_RISCV_CODE_MODEL = medany