Keep the Linux build free of curl, WebKitGTK and extra X11 packages

JUCE_USE_CURL defaults to 1 on Linux, so juce_core compiled
juce_Network_curl.cpp and included <curl/curl.h>. Nothing linked libcurl
(NEEDS_CURL was off), but its development headers were still a hard build
requirement. Set JUCE_USE_CURL=0 and pin NEEDS_CURL/NEEDS_WEB_BROWSER to
FALSE alongside the existing JUCE_WEB_BROWSER=0.

X11's Xrandr/Xinerama/Xshm/Xcursor headers are only dlsym()ed at runtime, but
live in separate -dev packages on Arch/Artix. Probe each with
check_include_file_cxx and define the JUCE_USE_* flags accordingly, so a
distro carrying just libX11 still builds.

Also check alsa/freetype2/fontconfig up front with a distro-specific hint
instead of letting JUCE's raw pkg-config error surface, and expand the
README's Linux section to cover all of it.

CMakeLists.txt

@@ -38,6 +38,12 @@ juce_add_plugin(GelykEQ
     BUNDLE_ID                   com.gelyk.eq
     JucePlugin_Name             "Gelyk EQ"
     JucePlugin_Desc             "A minimalist cyber/neon multiband equalizer"
+
+    # Never link libcurl or WebKitGTK. Gelyk does no networking and has no
+    # embedded browser, so both optional Linux dependency groups stay off.
+    # (juce_add_plugin leaves these unset = off, this is just explicit.)
+    NEEDS_CURL                  FALSE
+    NEEDS_WEB_BROWSER           FALSE
 )
 
 juce_generate_juce_header(GelykEQ)
@@ -106,7 +112,68 @@ target_compile_definitions(GelykEQ PRIVATE JUCE_MODULE_AVAILABLE_juce_dsp=1)
 # Otherwise juce_gui_extra's WebBrowserComponent pulls in WebKitGTK + GTK dev
 # headers (webkit2gtk, gtk, jsc, libsoup), which would break headless builds
 # like Arch/Artix where those aren't installed.
-target_compile_definitions(GelykEQ PRIVATE JUCE_WEB_BROWSER=0)
+#
+# JUCE_USE_CURL is the matching kill switch for juce_core: with it left at its
+# Linux default of 1, juce_core #includes <curl/curl.h> and compiles
+# juce_Network_curl.cpp, so libcurl *development headers* become a hard build
+# requirement even though nothing links libcurl (NEEDS_CURL is FALSE above).
+# Gelyk never uses URL/WebInputStream, so switching it off costs nothing.
+#
+# Native file dialogs are not a problem either: JUCE 8's Linux FileChooser
+# shells out to zenity/kdialog via ChildProcess instead of linking GTK, and
+# Gelyk never opens one.
+target_compile_definitions(GelykEQ PRIVATE
+    JUCE_WEB_BROWSER=0
+    JUCE_USE_CURL=0
+)
+
+# --- Linux / BSD only ---------------------------------------------------
+# The remaining Linux requirements are genuinely needed (X11 windowing, ALSA
+# and FreeType/fontconfig for juce_graphics text), but they arrive as several
+# separate -dev packages on Arch/Artix. Fail early with a useful hint instead
+# of JUCE's raw pkg-config error. Nothing below pulls in GTK/WebKitGTK/curl.
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux" OR CMAKE_SYSTEM_NAME MATCHES ".*BSD")
+    find_package(PkgConfig REQUIRED)
+    foreach(gelyk_dep alsa freetype2 fontconfig)
+        pkg_check_modules(GELYK_HAS_${gelyk_dep} QUIET ${gelyk_dep})
+        if(NOT GELYK_HAS_${gelyk_dep}_FOUND)
+            message(FATAL_ERROR
+                "Missing required Linux development package: '${gelyk_dep}'.\n"
+                "  Arch/Artix:   alsa-lib freetype2 fontconfig libx11\n"
+                "  Debian/Ubuntu: libasound2-dev libfreetype6-dev libfontconfig1-dev libx11-dev\n"
+                "  These are JUCE's own requirements (X11 windowing, ALSA, font rendering),\n"
+                "  not Gelyk's. No GTK, WebKitGTK, libcurl or file-selector package is needed.")
+        endif()
+    endforeach()
+
+    # X11's multi-monitor/DPI extensions are dlsym()ed at runtime by JUCE, so
+    # their headers are optional. Probe instead of hard-failing on distros that
+    # ship just libX11 + libXext (libXrandr/Xinerama/Xcursor are separate
+    # packages there). Only libX11's own headers are truly required.
+    include(CheckIncludeFileCXX)
+    set(gelyk_x11_optional
+        "JUCE_USE_XRANDR|X11/extensions/Xrandr.h"
+        "JUCE_USE_XINERAMA|X11/extensions/Xinerama.h"
+        "JUCE_USE_XSHM|X11/extensions/XShm.h"
+        "JUCE_USE_XCURSOR|X11/Xcursor/Xcursor.h"
+    )
+
+    set(gelyk_x11_defines)
+    foreach(gelyk_opt IN LISTS gelyk_x11_optional)
+        string(REPLACE "|" ";" gelyk_parts "${gelyk_opt}")
+        list(GET gelyk_parts 0 gelyk_define)
+        list(GET gelyk_parts 1 gelyk_header)
+        check_include_file_cxx("${gelyk_header}" GELYK_HAVE_${gelyk_define})
+        # A failed check leaves the variable empty rather than 0, which would
+        # end up as -DJUCE_USE_XCURSOR="" and break the preprocessor.
+        if(NOT GELYK_HAVE_${gelyk_define})
+            set(GELYK_HAVE_${gelyk_define} 0)
+        endif()
+        list(APPEND gelyk_x11_defines ${gelyk_define}=${GELYK_HAVE_${gelyk_define}})
+    endforeach()
+
+    target_compile_definitions(GelykEQ PRIVATE ${gelyk_x11_defines})
+endif()
 
 target_compile_options(GelykEQ PRIVATE
     $<$<CXX_COMPILER_ID:AppleClang,Clang>:-Wall -Wextra>