[ardour-dev] pthread_create discrepancy

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I hope this is the right place to ask about this problem.
if not, could someone point me in the right direction?

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ardour-0.9beta19
kernel 2.4.18
autoconf 2.52
automake 1.5
libtool 1.5.2

when i run configure for jack it says
# ./configure |grep pthread_create
checking for pthread_create... no
checking for pthread_create in -lpthread... yes

but when i configure in ardour, I get
# ./configure --prefix=/usr |grep pthread
configure: error: you have no POSIX thread support
checking for pthread_create in -lpthread... no
configure: error: /bin/sh './configure' failed for pbd
configure: error: /bin/sh './configure' failed for libs

ldconfig says
# ldconfig --verbose |grep pthread
	libpthread.so.0 -> libpthread-0.9.so
	libgnomevfs-pthread.so -> libgnomevfs-pthread.so

I assume that ardour bails here b/c it can't find 
pthread_create, but I don't understand how ardour and jack 
could disagree about it.  a search in libpthread-0.9.so found 
several instances of pthread_create.  if ardour is right, 
what library should be used to supply pthread_create?  
any advice at all would be _really_ appreciated.  
tia for any help.  

patrick