configure: allow user to specify --cross-cc-cflags-foo=

As an individual compiler may be able to support several targets with
the appropriate flags we need to expose this to the user as well.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>

configure

@@ -459,10 +459,14 @@ docker="no"
 
 # cross compilers defaults, can be overridden with --cross-cc-ARCH
 cross_cc_aarch64="aarch64-linux-gnu-gcc"
+cross_cc_aarch64_be="$cross_cc_aarch64"
+cross_cc_cflags_aarch64_be="-mbig-endian"
 cross_cc_arm="arm-linux-gnueabihf-gcc"
+cross_cc_cflags_armeb="-mbig-endian"
 cross_cc_i386="i386-pc-linux-gnu-gcc"
 cross_cc_cflags_i386=""
 cross_cc_powerpc="powerpc-linux-gnu-gcc"
+cross_cc_powerpc="powerpc-linux-gnu-gcc"
 
 enabled_cross_compilers=""
 
@@ -498,6 +502,9 @@ for opt do
   ;;
   --cross-cc-*[!a-zA-Z0-9_-]*=*) error_exit "Passed bad --cross-cc-FOO option"
   ;;
+  --cross-cc-cflags-*) cc_arch=${opt#--cross-cc-flags-}; cc_arch=${cc_arch%%=*}
+                      eval "cross_cc_cflags_${cc_arch}=\$optarg"
+  ;;
   --cross-cc-*) cc_arch=${opt#--cross-cc-}; cc_arch=${cc_arch%%=*}
                 eval "cross_cc_${cc_arch}=\$optarg"
   ;;
@@ -1527,6 +1534,7 @@ Advanced options (experts only):
   --extra-cxxflags=CXXFLAGS append extra C++ compiler flags QEMU_CXXFLAGS
   --extra-ldflags=LDFLAGS  append extra linker flags LDFLAGS
   --cross-cc-ARCH=CC       use compiler when building ARCH guest test cases
+  --cross-cc-flags-ARCH=   use compiler flags when building ARCH guest tests
   --make=MAKE              use specified make [$make]
   --install=INSTALL        use specified install [$install]
   --python=PYTHON          use specified python [$python]
@@ -6883,6 +6891,7 @@ case "$target_name" in
     mttcg="yes"
     gdb_xml_files="arm-core.xml arm-vfp.xml arm-vfp3.xml arm-neon.xml"
     target_compiler=$cross_cc_arm
+    eval "target_compiler_cflags=\$cross_cc_cflags_${target_name}"
   ;;
   aarch64|aarch64_be)
     TARGET_ARCH=aarch64
@@ -6891,6 +6900,7 @@ case "$target_name" in
     mttcg="yes"
     gdb_xml_files="aarch64-core.xml aarch64-fpu.xml arm-core.xml arm-vfp.xml arm-vfp3.xml arm-neon.xml"
     target_compiler=$cross_cc_aarch64
+    eval "target_compiler_cflags=\$cross_cc_cflags_${target_name}"
   ;;
   cris)
     target_compiler=$cross_cc_cris