add FITPACK Fortran library

start developing of FITPACK C++ bindings
mount_server.cpp: fix compilation error with GCC15

cxx/fitpack/fpgivs.f

@@ -0,0 +1,21 @@
+      recursive subroutine fpgivs(piv,ww,cos,sin)
+      implicit none
+c  subroutine fpgivs calculates the parameters of a givens
+c  transformation .
+c  ..
+c  ..scalar arguments..
+      real*8 piv,ww,cos,sin
+c  ..local scalars..
+      real*8 dd,one,store
+c  ..function references..
+      real*8 abs,sqrt
+c  ..
+      one = 0.1e+01
+      store = abs(piv)
+      if(store.ge.ww) dd = store*sqrt(one+(ww/piv)**2)
+      if(store.lt.ww) dd = ww*sqrt(one+(piv/ww)**2)
+      cos = ww/dd
+      sin = piv/dd
+      ww = dd
+      return
+      end