[Reproducible-builds] Bug#791517: FTBFS: missing dependency on something pkgconfig related

[Chris West (Faux)]

Source: easymp3gain
Version: 0.5.0+svn135-5
Severity: serious
Tags: sid
Justification: fails to build from source (but built successfully in the past)
User: reproducible-builds at lists.alioth.debian.org
Usertags: ftbfs

Dear Maintainer,

The package fails to build:
-- Compiling easyMp3Gain version 0.5.1
-- Found Gettext: /usr/bin/msgmerge (found version "0.19.4") 
CMake Error at /usr/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:138 (message):
  Could NOT find PkgConfig (missing: PKG_CONFIG_EXECUTABLE)
Call Stack (most recent call first):
  /usr/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:374 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-3.2/Modules/FindPkgConfig.cmake:48 (find_package_handle_standard_args)
  CMakeLists.txt:69 (find_package)
-- Configuring incomplete, errors occurred!

However, it passes on some of my test machines with other random sets of packages installed.

Full build log:
https://reproducible.debian.net/rb-pkg/unstable/amd64/easymp3gain.html

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 3.19.0-21-generic (SMP w/8 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)