updating the title to hopefully be more meaningful.

First, find the location of libcurl.pc; then set PKG_CONFIG_PATH
to the directory of that file.  E.g. if curl is installed in
opt/curl/, libcurl.pc is likely in opt/curl/lib/pkgconfig/, so do

PKG_CONFIG_PATH=/opt/curl/lib/pkgconfig/ ./configure …

thank you. The --with-curl issue is resolved by applying your recommendation however it appears that a number of switches are now "broken" in 7.4

--with-icu-dir, --enable-libxml, --enable-wddx, --enable-hash, --enable-curl, --with-gd, --with-jpeg-dir, --with-webp-dir, --with-freetype-dir, --with-libxml-dir, --enable-zip, --with-libzip, --with-pcre-regex, --with-pcre-dir

Unfortunately I can only set PKG_CONFIG_PATH once, which means that I then cant sort out ICU or any of the other compiled locations.

So it seems to me that a more workable approach in my scenario would be to use CURL_CFLAGS and CURL_LIBS instead of PKG_CONFIG_PATH. 

Then I could use  ICU_CFLAGS and ICU_LIBS for ICU and so on for all the other switches for which I need to set library location.

With this in mind I would greatly appreciate it if you could let me know what i would need to set 
CURL_CFLAGS and CURL_LIBS to.  (from what you tell me I will then work out what to set all the others to as I'm assuming the same conceptual approach would apply) 

thanks again!

> Unfortunately I can only set PKG_CONFIG_PATH once, […]

Indeed, but the variable has the same format as PATH, i.e. it
supports a colon delimited list of paths.

And of course, this needs to be documented in the PHP manual
proper (not only in the migration guide[1]).

[1] <https://www.php.net/manual/en/migration74.other-changes.php#migration74.other-changes.pkg-config>

I have copied all my *.pc files into a single PKGINFO directory and set PKG_CONFIG_PATH=${PKGINFO directory}

This seems to resolve all my --with-zzzzz issues, however now I am seeing the below issue (which is a provided PHP extension I can find under the PHP source folder). ...right now I can only assume the problem is being introduced because PKG_CONFIG_PATH has been set (as we have never seen this issue prior to 7.4)

I would really appreciate some help with this as it is causing real problems for our install. thanks

LATEST ERROR
------------

checking whether to enable multibyte string support... yes, shared
checking whether to enable multibyte regex support (requires oniguruma)... yes
checking for oniguruma... no
configure: error: Package requirements (oniguruma) were not met:

No package 'oniguruma' found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables ONIG_CFLAGS
and ONIG_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

> checking for oniguruma... no

[root@testserver:~]$ rpm -qa | grep onig
oniguruma-6.9.4-1.fc31.x86_64
oniguruma-devel-6.9.4-1.fc31.x86_64

just install or build it, it's no longer bundeled

PHP 7.4.3 built successfully using the

PKG_CONFIG_PATH=aaa:bbb:ccc:....

approach.

(and installing oniguruma-devel)

Thank you so much for all your help!

> PHP 7.4.3 built successfully […]

Great!