[php] Compiling php with curl, where is curl installed?

I need to specify a directory when compiling php with --with-curl=

The curl binary is located at /usr/bin/curl

curl -V gives me

curl 7.15.5 (x86_64-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5

locate curl gives me

/usr/bin/curl
/usr/lib/libcurl.so.3
/usr/lib/libcurl.so.3.0.0
/usr/lib64/libcurl.so.3
/usr/lib64/libcurl.so.3.0.0

removed /usr/share/... and other irrelevant files

UPDATE

Tried --with-curl=/usr/lib64 and --with-curl=/usr/lib although I'm pretty sure it's 64 bit.

checking for cURL support... yes
checking if we should use cURL for url streams... no
checking for cURL in default path... not found
configure: error: Please reinstall the libcurl distribution -
    easy.h should be in <curl-dir>/include/curl/

SOLUTION

PHP requires curl-devel

If you're going to compile a 64bit version(x86_64) of php use: /usr/lib64/

For architectures (i386 ... i686) use /usr/lib/

I recommend compiling php to the same architecture as apache. As you're using a 64bit linux i asume your apache is also compiled for x86_64.

For Ubuntu 17.0 +

Adding to @netcoder answer above, If you are using Ubuntu 17+, installing libcurl header files is half of the solution. The installation path in ubuntu 17.0+ is different than the installation path in older Ubuntu version. After installing libcurl, you will still get the "cURL not found" error. You need to perform one extra step (as suggested by @minhajul in the OP comment section).

Add a symlink in /usr/include of the cURL installation folder (cURL installation path in Ubuntu 17.0.4 is /usr/include/x86_64-linux-gnu/curl).

My server was running Ubuntu 17.0.4, the commands to enable cURL support were

sudo apt-get install libcurl4-gnutls-dev

Then create a link to cURL installation

cd /usr/include
sudo ln -s x86_64-linux-gnu/curl

Try just --with-curl, without specifying a location, and see if it'll find it by itself.

php curl lib is just a wrapper of cUrl, so, first of all, you should install cUrl. Download the cUrl source to your linux server. Then, use the follow commands to install:

tar zxvf cUrl_src_taz
cd cUrl_src_taz
./configure --prefix=/curl/install/home
make
make test    (optional)
make install
ln -s  /curl/install/home/bin/curl-config /usr/bin/curl-config

Then, copy the head files in the "/curl/install/home/include/" to "/usr/local/include". After all above steps done, the php curl extension configuration could find the original curl, and you can use the standard php extension method to install php curl.
Hope it helps you, :)