gitcompile: restore ACLOCAL_FLAGS ability to use

gitcompile: restore ACLOCAL_FLAGS ability to use

Fixes cryptic "error macro 'AM_PATH_ALSA' not found in library
configure.ac:22" when attempting a local install as described at
https://thesofproject.github.io/latest/getting_started/build-guide/build-from-scratch.html#build-alsa-lib-and-alsa-utils-from-source

Fixes giant commit f9e6010d5ec7 ("topology: plugins - add Intel nhlt
encoder plugin") which added a second invocation of `aclocal` in 2021
but forgot the extra `$alsa_m4_flags`.

To avoid duplication, do not fix by adding the missing `$alsa_m4_flags`
to the second aclocal invocation. Instead, drop that variable and append
`-I ../alsa-lib/utils` directly to $ACLOCAL_FLAGS

Closes: https://github.com/alsa-project/alsa-utils/pull/272
Signed-off-by: Marc Herbert <marc.herbert@intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>