Build failure with this morning's R-alpha

| Trying to build a Debian snapshot of R-alpha based on last night's tarball,
| it fails with what looks like a missing -lm linking directive:
| 
| [...]
| gcc     -I. -I../../src/include -I../../src/include  -DHAVE_CONFIG_H  -fpic  -O2  -c Rmain.c -o Rmain.o
| gcc -Wl,--export-dynamic  -o R.bin Rmain.o  -L../../lib -lR
| ../../lib/libR.so: undefined reference to `isfinite'

Entirely my fault -- I had been resetting CFLAGS and friends in debian/rules,
which lead to the all-important  -std=gnu99   being dropped from the compiler
flags.  And gcc up to version 3.4.* seems to forgive this, whereas 4.*
versions want it.  

Thanks, Dirk

Hell, there are no rules here - we're trying to accomplish something. 
                                                  -- Thomas A. Edison