Parallel Build Fails

[sanssecours]

Issue Description

While creating a Homebrew formula for YAEP, I noticed that building the software in parallel fails sometimes.

Steps to Reproduce

mkdir build
cd build
# I use Ninja (https://ninja-build.org) below, since it seems to
# fail consistently (unlike e.g. `make` using the switch `-j9`, 
# which only fails sometimes).
cmake -GNinja .. 
ninja

Expected Result

The build system creates the library without any problems.

Actual Result

Ninja prints the following error message:

[12/211] Building C object src/CMakeFiles/yaep_test.dir/yaep.c.o
FAILED: src/CMakeFiles/yaep_test.dir/yaep.c.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc  -Isrc -DYAEP_TEST -DYAEP_DEBUG -std=gnu90 -MD -MT src/CMakeFiles/yaep_test.dir/yaep.c.o -MF src/CMakeFiles/yaep_test.dir/yaep.c.o.d -o src/CMakeFiles/yaep_test.dir/yaep.c.o   -c ../src/yaep.c
../src/yaep.c:3497:10: fatal error: 'sgramm.c' file not found
#include "sgramm.c"
         ^~~~~~~~~~
1 error generated.
[16/211] Building CXX object src/CMakeFiles/yaep++_test.dir/yaep.cpp.o
FAILED: src/CMakeFiles/yaep++_test.dir/yaep.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -Isrc -DYAEP_TEST -DYAEP_DEBUG -std=gnu++11 -MD -MT src/CMakeFiles/yaep++_test.dir/yaep.cpp.o -MF src/CMakeFiles/yaep++_test.dir/yaep.cpp.o.d -o src/CMakeFiles/yaep++_test.dir/yaep.cpp.o -c ../src/yaep.cpp
In file included from ../src/yaep.cpp:61:
In file included from ../src/yaep.c:3497:
build/src/sgramm.c:398:2: error: unterminated conditional directive
#if (! defined yyoverflow \
 ^
../src/yaep.cpp:99:10: error: use of undeclared identifier 'yaep_parse_grammar'
  return yaep_parse_grammar (this->grammar, strict_p, description);
         ^
2 errors generated.
[18/211] [BISON][bison_ansic] Building parser with bison 3.2.2
ansic.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
ninja: build stopped: subcommand failed.

.

Additional Information

• OS: macOS 10.14.1
• CMake: cmake version 3.13.1