detect_cc: Handle empty arguments

When called from scripts, sometimes the arguments passed
will be empty.

Change-Id: I2f9fa1daa173eecc7b20928cd359284bb6f74ff3
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.gerrithub.io/c/444278
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>

scripts/detect_cc.sh

@@ -23,10 +23,7 @@ function usage()
 	err " --lto=[y|n]               Attempt to configure for LTO"
 }
 
-CC=cc
-CXX=c++
-LD=ld
-LTO=n
+
 
 for i in "$@"; do
 	case "$i" in
@@ -35,16 +32,24 @@ for i in "$@"; do
 			exit 0
 			;;
 		--cc=*)
+			if [[ -n "${i#*=}" ]]; then
 				CC="${i#*=}"
+			fi
 			;;
 		--cxx=*)
+			if [[ -n "${i#*=}" ]]; then
 				CXX="${i#*=}"
+			fi
 			;;
 		--lto=*)
+			if [[ -n "${i#*=}" ]]; then
 				LTO="${i#*=}"
+			fi
 			;;
 		--ld=*)
+			if [[ -n "${i#*=}" ]]; then
 				LD="${i#*=}"
+			fi
 			;;
 		--)
 			break
@@ -56,6 +61,11 @@ for i in "$@"; do
 	esac
 done
 
+: ${CC=cc}
+: ${CXX=c++}
+: ${LD=ld}
+: ${LTO=n}
+
 CC_TYPE=$($CC -v 2>&1 | grep -o -E '\w+ version' | head -1 | awk '{ print $1 }')
 CXX_TYPE=$($CXX -v 2>&1 | grep -o -E '\w+ version' | head -1 | awk '{ print $1 }')
 if [ "$CC_TYPE" != "$CXX_TYPE" ]; then