linux-armv6: install newer CMake from buster-backports (lovell#306)

Author: kleisauke

build/posix.sh

@@ -127,8 +127,6 @@ fi
 mkdir ${DEPS}/zlib-ng
 $CURL https://github.com/zlib-ng/zlib-ng/archive/${VERSION_ZLIB_NG}.tar.gz | tar xzC ${DEPS}/zlib-ng --strip-components=1
 cd ${DEPS}/zlib-ng
-# Downgrade minimum required CMake version to 3.13 - https://github.com/zlib-ng/zlib-ng/pull/2001
-sed -i'.bak' "/^cmake_minimum_required/s/3.14/3.13/" CMakeLists.txt
 CFLAGS="${CFLAGS} -O3" cmake -G"Unix Makefiles" \
   -DCMAKE_TOOLCHAIN_FILE=${ROOT}/Toolchain.cmake -DCMAKE_INSTALL_PREFIX=${TARGET} -DCMAKE_INSTALL_LIBDIR=lib -DCMAKE_BUILD_TYPE=Release \
   -DBUILD_SHARED_LIBS=FALSE -DBUILD_TESTING=FALSE -DZLIB_COMPAT=TRUE -DWITH_ARMV6=FALSE
@@ -176,8 +174,6 @@ meson install -C _build --tag devel
 mkdir ${DEPS}/aom
 $CURL https://storage.googleapis.com/aom-releases/libaom-${VERSION_AOM}.tar.gz | tar xzC ${DEPS}/aom --strip-components=1
 cd ${DEPS}/aom
-# Downgrade minimum required CMake version to 3.13 - https://aomedia.googlesource.com/aom/+/597a35fbc9837e33366a1108631d9c72ee7a49e7
-find . -name 'CMakeLists.txt' -o -name '*.cmake' | xargs sed -i'.bak' "/^cmake_minimum_required/s/3.16/3.13/"
 # [PATCH] cmake: fix nasm detection w/3.0
 $CURL https://github.com/m-ab-s/aom/commit/6d2b7f71b98bfa28e372b1f2d85f137280bdb3de.patch | patch -p1
 mkdir aom_build
@@ -193,8 +189,6 @@ make install/strip
 mkdir ${DEPS}/heif
 $CURL https://github.com/strukturag/libheif/releases/download/v${VERSION_HEIF}/libheif-${VERSION_HEIF}.tar.gz | tar xzC ${DEPS}/heif --strip-components=1
 cd ${DEPS}/heif
-# Downgrade minimum required CMake version to 3.13 - https://github.com/strukturag/libheif/issues/975
-sed -i'.bak' "/^cmake_minimum_required/s/3.16.3/3.13/" CMakeLists.txt
 CFLAGS="${CFLAGS} -O3" CXXFLAGS="${CXXFLAGS} -O3" cmake -G"Unix Makefiles" \
   -DCMAKE_TOOLCHAIN_FILE=${ROOT}/Toolchain.cmake -DCMAKE_INSTALL_PREFIX=${TARGET} -DCMAKE_INSTALL_LIBDIR=lib -DCMAKE_BUILD_TYPE=Release \
   -DBUILD_SHARED_LIBS=FALSE -DBUILD_TESTING=0 -DENABLE_PLUGIN_LOADING=0 -DWITH_EXAMPLES=0 -DWITH_LIBDE265=0 -DWITH_X265=0

platforms/linux-armv6/Dockerfile

@@ -11,14 +11,14 @@ ENV \
 
 # Build dependencies
 RUN \
+  echo "deb http://archive.debian.org/debian buster-backports main" >> /etc/apt/sources.list.d/backports.list && \
   apt-get update && \
   apt-get install -y curl && \
   dpkg --add-architecture armhf && \
   apt-get update && \
   apt-get install -y \
     autoconf \
     autopoint \
-    cmake \
     gettext \
     git \
     gperf \
@@ -29,6 +29,7 @@ RUN \
     pkg-config \
     python3-pip \
     && \
+  apt-get install -y -t buster-backports cmake && \
   mkdir /root/tools && \
   curl -Ls https://github.com/rvagg/rpi-newer-crosstools/archive/master.tar.gz | tar xzC /root/tools --strip-components=1 && \
   curl https://sh.rustup.rs -sSf | sh -s -- -y \