arm64: Avoid setting march to corei7 when Cross Compiling for ARM

  When Cross-compiling VPP for arm64 target and build machine is x86_64,
  based on build_cpu value, the march variable is set to corei7 which is
  an unrecoganized option for ARM tool chain.
  This breaks the VPP compilation.

Change-Id: I4cba5b4990e7cf0bdc1403e90c3d18110900bbef
Signed-off-by: Sachin Saxena <sachin.saxena@nxp.com>
diff --git a/src/configure.ac b/src/configure.ac
index 2a54cd2..ca967bb 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -172,7 +172,7 @@
   [march_skylake_avx512=no])
 AM_CONDITIONAL([CC_SUPPORTS_AVX512], [test "$march_skylake_avx512" = "yes"])
 
-AS_CASE([$build_cpu],
+AS_CASE([$host_cpu],
 	[x86_64], [CPU_FLAGS="-march=corei7 -mtune=corei7-avx"],
 	[aarch64], [CPU_FLAGS="-march=armv8-a+crc"],
 	[CPU_FLAGS=""],
@@ -182,8 +182,8 @@
 AC_SUBST([CPU_AVX2_FLAGS],"-march=core-avx2 -mtune=core-avx2")
 AC_SUBST([CPU_AVX512_FLAGS],"-march=skylake-avx512 -mtune=skylake-avx512")
 
-AM_CONDITIONAL([CPU_X86_64], [test "$build_cpu" = "x86_64"])
-AM_CONDITIONAL([CPU_AARCH64], [test "$build_cpu" = "aarch64"])
+AM_CONDITIONAL([CPU_X86_64], [test "$host_cpu" = "x86_64"])
+AM_CONDITIONAL([CPU_AARCH64], [test "$host_cpu" = "aarch64"])
 
 ###############################################################################
 # misc compiler flags