webkitgtk: fix build failure with DEBUG_BUILD enabled

webkitgtk: fix build failure with DEBUG_BUILD enabled

It fails to compile webkitgtk when debug build enabled:

| /path_to/tmp/work/core2-64-poky-linux/webkitgtk/2.40.5/webkitgtk-2.40.5/Source/bmalloc/libpas/src/libpas/pas_allocation_result.h:76:1:
  error: inlining failed in call to 'always_inline' 'pas_allocation_result pas_allocation_result_identity(pas_allocation_result)':
  function not considered for inlining
|    76 | pas_allocation_result_identity(pas_allocation_result result)
|       | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Add a cmake variable WEBKIT_NO_INLINE_HINTS to disable gcc function
attribute `always_inline` when debug build is enabled.

And adjust indent as well.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>