Fix compilation error with empty CFLAGS of GLESv1-CM and GLESv2

When cross-compiling yagears on my x86-64 host machine for a 32-bit RISC-V Buildroot Linux target, I encountered the following error:

FAILED: libyagears.a.p/gears_engine.c.o 
riscv32-buildroot-linux-gnu-gcc -Ilibyagears.a.p -I. -I../.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall 
-Winvalid-pch -O0 -g -D_GNU_SOURCE -DENGINE_CTOR -fPIC '' '-DGLESV2_H=<GLES2/gl2.h>' '
-DGLESV2_LIB="libGLESv2.so.2"' '' '-DGLESV1_CM_H=<GLES/gl.h>' '-DGLESV1_CM_LIB="libGLESv1_CM.so.1"' 
-MD -MQ libyagears.a.p/gears_engine.c.o -MF libyagears.a.p/gears_engine.c.o.d -o libyagears.a.p/gears_engine.c.o
-c ../../gears_engine.c
riscv32-buildroot-linux-gnu-gcc.br_real: warning: : linker input file unused because linking not done
riscv32-buildroot-linux-gnu-gcc.br_real: error: : linker input file not found: No such file or directory
riscv32-buildroot-linux-gnu-gcc.br_real: warning: : linker input file unused because linking not done

Upon investigation, I found the root cause to be the '' (empty quotes) between -DGLESV2_LIB="libGLESv2.so.2" and -DGLESV1_CM_H=<GLES/gl.h>, passed to the riscv32-buildroot-linux-gnu-gcc command. These empty quotes were generated by the following two lines in the meson.build:

glesv1_cm_dep = declare_dependency(compile_args: run_command('pkg-config', '--cflags', 'glesv1_cm', check: true).stdout().strip().split(' '))
...
glesv2_dep = declare_dependency(compile_args: run_command('pkg-config', '--cflags', 'glesv2', check: true).stdout().strip().split(' '))

I realized the issue was that pkg-config returned empty CFLAGS for GLESv1-CM and GLESv2 in my Buildroot environment. Although these libraries are installed, no CFLAGS were necessary.

To resolve this, I propose checking if the CFLAGS returned by pkg-config for GLESv1_CM and GLESv2 are empty before passing them to the dependency variables. This will prevent unnecessary empty strings from being passed to the compiler.

caramelli / yagears

Fix compilation error with empty CFLAGS of GLESv1-CM and GLESv2 #3