Revert "_build.sh: apply mman.h hack to alpine+gcc"

This reverts commit d2d78d5.

_build.sh

@@ -999,22 +999,17 @@ build_single_target() {
     _BINUTILS_SUFFIX="${_CCSUFFIX}"
   fi
 
-  if [ "${_CRT}" = 'musl' ]; then
+  if [ "${_CRT}" = 'musl' ] && [ "${_DISTRO}" = 'debian' ]; then
     if [ "${_OPENSSL}" = 'quictls' ] || \
        [ "${_OPENSSL}" = 'openssl' ]; then
-      mman_hack=0
-      [ "${_DISTRO}" = 'debian' ] && mman_hack=1
-      [ "${_DISTRO}" = 'alpine' ] && [ "${_CC}" = 'gcc' ] && mman_hack=1
-      if [ "${mman_hack}" = '1' ]; then
-        # Workaround for:
-        #   ../crypto/mem_sec.c:60:13: fatal error: linux/mman.h: No such file or directory
-        # Based on: https://github.com/openssl/openssl/issues/7207#issuecomment-880121450
-        _my_incdir='_sys_include'; rm -r -f "${_my_incdir}"; mkdir "${_my_incdir}"; _my_incdir="$(pwd)/${_my_incdir}"
-        ln -s "/usr/include/${_TRIPLETSH}/asm" "${_my_incdir}/asm"
-        ln -s "/usr/include/asm-generic"       "${_my_incdir}/asm-generic"
-        ln -s "/usr/include/linux"             "${_my_incdir}/linux"
-        _CPPFLAGS_GLOBAL="${_CPPFLAGS_GLOBAL} -isystem ${_my_incdir}"
-      fi
+      # Workaround for:
+      #   ../crypto/mem_sec.c:60:13: fatal error: linux/mman.h: No such file or directory
+      # Based on: https://github.com/openssl/openssl/issues/7207#issuecomment-880121450
+      _my_incdir='_sys_include'; rm -r -f "${_my_incdir}"; mkdir "${_my_incdir}"; _my_incdir="$(pwd)/${_my_incdir}"
+      ln -s "/usr/include/${_TRIPLETSH}/asm" "${_my_incdir}/asm"
+      ln -s "/usr/include/asm-generic"       "${_my_incdir}/asm-generic"
+      ln -s "/usr/include/linux"             "${_my_incdir}/linux"
+      _CPPFLAGS_GLOBAL="${_CPPFLAGS_GLOBAL} -isystem ${_my_incdir}"
     fi
   fi