CMake/QtAutoDetect: fix failure with multiline toolchain file

The unquoted 'string(FIND ${toolchain_file_content} ...)' call fails for
multiline content of the variable toolchain_file_content, so add
quotes around, fixes:

  [...]
  CMake Error at cmake/QtAutoDetect.cmake:42 (string):
    string sub-command FIND requires 3 or 4 parameters.
  Call Stack (most recent call first):
    cmake/QtAutoDetect.cmake:311 (qt_auto_detect_android)
    CMakeLists.txt:19 (include)
  [...]
  -- Configuring incomplete, errors occurred!

in case the given toolchain file starts with multiple lines
in the first 80 characters, e.g. in the case of buildroot:

  #
  # Automatically generated file; DO NOT EDIT.
  # CMake toolchain file for Buildroot
  #
  [...]

Task-number: QTBUG-90980
Pick-to: 6.0 6.1
Change-Id: I8e038e08d83016e8253f2e83b2efb8f06034c6cd
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

0 files changed, 0 insertions, 0 deletions