Modify armv7 -march in cmake

armv7 build failure was seen with gcc 11. armv7-a target no longer
includes an FPU by default, so we need to specify -march=armv7-a+fp.
However, armv7-a+fp isn't supported in old gcc version(e.g. gcc-5.4).
To accommodate that, use -mfpu=vfpv3 instead.

BUG=aomedia:3226

Change-Id: I13afa284d881c4a5d83675e1b9fb1af8c45480af
(cherry picked from commit 1908972c6f3dae585f88185cbaa7e921ddfcdbb3)

build/cmake/toolchains/armv7-linux-gcc.cmake

diff --git a/build/cmake/toolchains/armv7-linux-gcc.cmake b/build/cmake/toolchains/armv7-linux-gcc.cmake
index b898b4b..0a2fca1 100644
--- a/build/cmake/toolchains/armv7-linux-gcc.cmake
+++ b/build/cmake/toolchains/armv7-linux-gcc.cmake
@@ -28,8 +28,10 @@
 set(CMAKE_C_COMPILER ${CROSS}gcc)
 set(CMAKE_CXX_COMPILER ${CROSS}g++)
 set(AS_EXECUTABLE ${CROSS}as)
-set(CMAKE_C_COMPILER_ARG1 "-march=armv7-a ${AOM_EXTRA_TOOLCHAIN_FLAGS}")
-set(CMAKE_CXX_COMPILER_ARG1 "-march=armv7-a ${AOM_EXTRA_TOOLCHAIN_FLAGS}")
+set(CMAKE_C_COMPILER_ARG1 "-march=armv7-a -mfpu=vfpv3 \
+                          ${AOM_EXTRA_TOOLCHAIN_FLAGS}")
+set(CMAKE_CXX_COMPILER_ARG1 "-march=armv7-a -mfpu=vfpv3 \
+                            ${AOM_EXTRA_TOOLCHAIN_FLAGS}")
 set(AOM_AS_FLAGS --defsym ARCHITECTURE=7 -march=armv7-a -mfpu=neon
                  ${AOM_EXTRA_TOOLCHAIN_FLAGS})
 set(CMAKE_SYSTEM_PROCESSOR "armv7")